Sierra Sleep by Ashley
Sierra Sleep Millennium Luxury Gel Memory Foam Mattress
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The Sierra Sleep Millennium Luxury Gel Memory Foam Mattress is a straightforward pick if what you want is a supportive, tight top surface with real cooling built into the foam itself, not just a name on the label.
Construction
This is a 14 inch, all-foam mattress from Sierra Sleep, Ashley's in-house mattress brand, built on the M505 platform. Under the 4-way stretch knit cover sit two layers of phase change material woven into the fabric itself, so the surface starts working on temperature the moment you lie down.
- 2 inches of copper-infused gel memory foam at the top, for the first layer of body contouring
- 1.5 inches of charcoal-infused gel memory foam underneath, pulling heat and moisture away from the surface
- 3 inches of sculpted, body-contouring comfort foam beneath that
- A green tea-infused support foam base carrying the remaining height and keeping the mattress fresh over years of use
Because it ships compressed in a box, give it roughly 48 hours after unboxing before you judge the feel. Foam needs that window to fully expand and settle into its true loft.
Feel and Support
Ashley rates the comfort level here as cushion firm: a tight top surface with just enough give at the shoulder and hip to soften contact, but no deep, slow sinking. The three layered foams handle the contouring up top, while the support base underneath keeps the mattress from bottoming out under sustained weight. There's no coil system anywhere in this build, so what quiet you get comes from the foam itself. No springs to creak, and less chance a partner's movement travels across to your side of the bed.
Who It's For
Back and combination sleepers tend to do well here: cushion firm keeps the spine level while still giving a little at the pressure points as you shift position through the night. Side sleepers who want more structure than a plush mattress but still want some cushion at the shoulder are also a good match. Sleepers who run warm at night are exactly who the copper and charcoal-infused foam layers and the phase change cover are built for.
Skip it if you're a dedicated stomach sleeper looking for a flat, minimal-give surface, or if you specifically want the bounce and airflow of a coil hybrid. This is a foam mattress through and through. It is adjustable base compatible, so it works on a platform frame now and an adjustable base later without any change in performance.
Available sizes: Twin XL, Queen, King, and California King. This is the Millennium Luxury Gel Memory Foam mattress, Ashley model M505, and the only real way to know if cushion firm is your firm is to lie down on it. Come test it in person at one of our Kentucky showrooms before you decide.
What makes this mattress different
Cushion firm, tight top feel
A supportive tight top surface with just enough give at the shoulder and hip, built for sleepers who want structure underneath without a hard, flat surface on top.
Copper-infused gel memory foam
Two inches of copper-infused gel memory foam forms the first comfort layer, contouring to the body at the surface.
Charcoal-infused gel memory foam
A layer and a half of charcoal-infused gel memory foam sits underneath, working to pull heat and moisture away from the surface through the night.
Two layers of phase change material
Built into the 4-way stretch knit cover itself, two layers of phase change material start regulating temperature the moment you lie down, not just at the foam level.
Sculpted body-contouring comfort foam
A third foam layer, three inches of sculpted comfort foam, adds cushioning between the cooling layers above and the support base below.
Green tea-infused support foam base
The foundation layer is infused with green tea, which helps the mattress stay fresh over years of regular use while carrying most of the mattress's support.
Adjustable base compatible
Works on a platform frame now and an adjustable base later without any change in performance, so the mattress isn't locked to one setup.
Ships in a box, ready in about 48 hours
Arrives compressed for delivery. Give it roughly two days after unboxing to fully expand before judging the feel.
Three foam layers and a cooling cover, stacked for a supportive tight top feel
The Millennium Luxury Gel Memory Foam Mattress is a 14 inch, all-foam build with no coil unit anywhere in the construction. From the top down: a 4-way stretch knit cover with two layers of phase change material woven in, then 2 inches of copper-infused gel memory foam, then 1.5 inches of charcoal-infused gel memory foam, then 3 inches of sculpted, body-contouring comfort foam. A green tea-infused support foam base carries the remaining height and keeps the mattress fresh over years of use.
Each layer has a job. The copper-infused foam does the initial contouring at the surface, the charcoal-infused layer and the phase change cover work together to move heat and moisture away before they build up, and the sculpted comfort foam underneath adds cushioning without letting the whole mattress feel soft. The support base is what keeps the tight top surface from bottoming out under sustained weight, which is what gives this mattress its cushion firm comfort level: supportive first, with just enough give layered on top.
See the full Sierra Sleep lineup →Built for the back sleeper who wants a cooler, more supportive night
Back sleepers: a cushion firm tight top keeps the spine level while the copper-infused top layer contours just enough at the shoulder and hip. This is the easiest yes on this mattress.
Combination sleepers: the layered foam gives a little as you shift position through the night without ever feeling like you're sinking into the mattress.
Side sleepers who want more structure than plush: there's cushioning at the surface, but this build leans firmer than a true plush mattress. If you want a deep cradle at the shoulder, look at a softer model in our lineup instead.
Hot sleepers: this is close to a purpose-built pick. The copper and charcoal-infused foam layers plus the phase change material in the cover are all aimed at the same problem, foam that traps heat, and stack three separate defenses against it.
Couples sharing a bed: an all-foam build with no coil unit means less chance a partner's movement travels across to your side.
Probably not for you if: you're a dedicated stomach sleeper who wants a flat, minimal-give surface, or you specifically want the bounce and airflow of a coil hybrid. This mattress is foam through and through.
Specifications
| Height | 14 in |
|---|---|
| Feel | Cushion Firm |
| Firmness | Cushion firm: a supportive tight top surface with contouring give at the shoulder and hip, not a deep plush sink |
| Construction | 4-way stretch knit cover with two layers of phase change material, over 2 in of copper-infused gel memory foam, 1.5 in of charcoal-infused gel memory foam, and 3 in of sculpted body-contouring comfort foam, over a green tea-infused support foam base. All-foam build, no coil unit, 14 in total. |
| Cooling | Two layers of phase change material in the cover, a copper-infused gel memory foam comfort layer, and a charcoal-infused gel memory foam layer underneath work together to move heat and moisture away from the surface. |
| Motion isolation | Very good. There's no coil unit in this all-foam build, so movement is absorbed within the foam layers themselves rather than traveling across the bed to a partner's side. |
| Warranty | 10-year non-prorated warranty |
Frequently asked questions
What does "cushion firm" mean on the Millennium Luxury Gel Memory Foam Mattress?
It describes a tight top surface that leans supportive rather than plush: firm enough to keep the spine level, with just enough give in the three foam layers on top to soften contact at the shoulder and hip. It's not a deep, slow-sinking feel.
Is this an all-foam mattress or does it have coils?
All-foam, no coil unit anywhere in the build. The 14 inch profile is made up of copper-infused gel memory foam, charcoal-infused gel memory foam, sculpted comfort foam, and a green tea-infused support foam base.
Who sleeps best on this mattress?
Back and combination sleepers tend to do best, since the cushion firm feel keeps the spine level while still giving at the pressure points as you shift position. Side sleepers who like some structure under a bit of cushion are also a good fit; dedicated stomach sleepers and anyone who wants a deep plush cradle should look elsewhere.
Does this mattress sleep cool?
That's the focus of the build. Two layers of phase change material are woven into the cover itself, copper-infused gel memory foam sits at the surface, and a charcoal-infused gel memory foam layer works underneath to pull heat and moisture away. Three separate layers are aimed at the same job.
How much motion transfer will I feel from a partner?
Less than an innerspring mattress. There's no coil unit in this build, so movement is absorbed within the foam layers themselves rather than traveling across springs to the other side of the bed.
Can I use this mattress on an adjustable base?
Yes. The all-foam construction is adjustable-base compatible, and it also sits well on a standard platform frame if that's what you have now and an adjustable base is a later upgrade.
Does the Millennium Luxury Gel Memory Foam Mattress come with an at-home trial?
No. Sierra Sleep beds, including this one, don't include an at-home trial or comfort exchange period. The honest way to know if cushion firm is your feel is to lie down on it in your own sleeping position at one of our Kentucky showrooms before you buy.
Can I see this mattress in person near me?
Yes, and with a mattress that's always the better way to decide. Mattress Overstock is a Kentucky-owned company with showrooms in Lexington, Georgetown, Somerset, London, and Richmond. Come lie on the Millennium Luxury Gel Memory Foam Mattress in your own sleeping position, and because everyone on our floor is paid the same no matter which brand you choose, the guidance you get is honest.
Buy it from people you can actually visit
- Free local delivery To your home across Central & Eastern Kentucky.
- Free setup We place and set up your new bed in the room.
- Free old-mattress haul-away The old one goes out the same day the new one comes in.
Independently owned in Kentucky since 2012. Walk in any day (no appointment) and someone who actually knows the floor will help you find the right fit.
Still deciding?
Try it in person at any Kentucky showroom
Walk into any Mattress Overstock location, lie down, and feel the difference yourself. No appointment, no pressure. Our team has over 100 years of combined mattress experience and we're here to help you find the right fit.
