Sierra Sleep by Ashley
Sierra Sleep Millennium 2.0 Foam 12 Inch Mattress
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The Millennium 2.0 is Sierra Sleep's answer for sleepers who want a firm, all-foam mattress that holds its shape all night, no coils, no bounce, just steady support from edge to edge. If "supportive" is the first word you reach for when describing your ideal bed, this is the Ashley model to lie on first.
How It's Built
Ashley builds the M311 as a firm, no-frills three-layer stack. A gel memory foam layer sits on top, taking the sharp edge off pressure points at the shoulders and hips while keeping the surface firm rather than plush. Underneath, a high-density support foam layer contours just enough to hold your spine in a stable line without letting the middle of the bed give way. A green tea infused foam base carries the load at the bottom, adding structure that keeps the full 12 inch build from breaking down early.
The cover is a Hyper Cool 4 way stretch knit, made with a phase changing material that pulls heat away from the body on contact. Paired with the gel memory foam layer, it keeps a firm all-foam bed from sleeping as warm as older foam builds tend to.
Feel and Support
This is a genuinely firm mattress, not a "firm" that softens the moment you lie down. Back and stomach sleepers tend to do best here: the firm surface keeps hips lifted and the spine level instead of letting it sag in the middle. Side sleepers who want real structure underneath them, rather than a deep hug at the shoulder, also tend to land well on the Millennium 2.0. Because it is all foam with no coils, motion transfer is close to zero, so a partner getting in late or rolling over is unlikely to wake you.
Who Should Look Elsewhere
If you sleep mainly on your side and want foam to cradle your shoulder and hip, the firm surface here will likely feel too hard for you; a plusher model in the Sierra Sleep lineup will serve you better. Sleepers who run warm at night may also prefer a hybrid with more airflow, since any all-foam build, even a cooling one, holds a bit more heat than a coil mattress does.
Good to Know
- Made in the USA
- Ships compressed in a box; allow up to 48 hours after unboxing for the mattress to fully expand
- Compatible with adjustable bases
- Available in Twin XL, Full, Queen, King, and California King
The Millennium 2.0 Foam 12 Inch is a straightforward, honest firm mattress: no coils to wear out, no plush layer to compress over time, just a stable foam bed built to hold its shape year after year. Come lie on it at one of our Kentucky showrooms in your own sleep position before you decide; a firm mattress is one you want to feel for yourself, not guess at from a description.
What makes this mattress different
Genuinely firm, not firm-ish
No mid-bed give and no plush top layer to compress. The surface stays firm the way Ashley built it, night after night.
Gel memory foam comfort layer
A gel memory foam layer takes the sharp edge off pressure at the shoulders and hips without softening the overall firm feel.
High-density support foam
Contours just enough to hold your spine level while keeping the surface stable under your weight.
Green tea infused foam base
Anchors the mattress at the bottom, adding structure that helps the 12 inch build hold its shape over time.
Hyper Cool 4-way stretch cover
A phase-changing knit cover pulls heat away from the body on contact, so a firm foam bed does not sleep as warm as older foam builds.
Zero-bounce, all-foam build
No coils means minimal motion transfer, so a partner rolling over or getting up late is unlikely to wake you.
Adjustable-base compatible
The all-foam construction flexes cleanly with a power base if you like to raise your head or feet.
Ships compressed, ready fast
Boxed for delivery and compressed for the trip. Allow up to 48 hours after unboxing for it to fully expand.
A firm foam stack built to hold its shape, not soften over time
From the top down, the Millennium 2.0 runs a Hyper Cool 4-way stretch knit cover, built with a phase-changing material that pulls heat away from the surface on contact. Under that sits a gel memory foam layer, kept thin enough to hold the bed firm while still taking the hard edge off pressure at the shoulders and hips.
The support comes from a high-density support foam layer beneath the comfort foam, contouring just enough to keep your spine level without letting the middle of the mattress give way. A green tea infused foam base carries the rest of the load at the bottom, anchoring the build and adding the long-term structure that keeps a firm mattress firm instead of breaking down early. There are no coils in this construction: the firmness comes from a shallow comfort layer over a stable foam foundation, not springs. The whole stack runs 12 inches, a lean profile that dresses with standard sheets and sits well on a platform, a solid foundation, or an adjustable base.
See the full Sierra Sleep lineup →Built for the back and stomach sleeper who wants real support
Back sleepers: firm support keeps your hips lifted and your spine level, the setup back sleepers tend to rest best on.
Stomach sleepers: this is the position that benefits most from firm. A softer bed lets the hips sink and the lower back arch; the Millennium 2.0 keeps you level instead.
Side sleepers who like structure: if you want a bed that holds you up rather than cradles you, the firm surface here can work, though a plusher model will feel more forgiving at the shoulder.
Couples and light sleepers: the all-foam build with no coils absorbs movement before it crosses the mattress, so a partner shifting or getting up does not travel to your side.
People who already know they like firm: if you have tried softer beds and kept waking up sore, or you simply prefer sleeping on top of a mattress instead of in it, this is a straightforward fit.
Probably not for you if: you are a dedicated side sleeper who wants deep pressure relief at the shoulder and hip, or you run cold and want the extra bounce and airflow of a coil hybrid. Ask the showroom team about a softer option in the Sierra Sleep lineup.
Specifications
| Height | 12 in |
|---|---|
| Feel | Firm |
| Firmness | Firm, a supportive surface with minimal give |
| Construction | Hyper Cool 4-way stretch knit cover over a gel memory foam layer, a high-density support foam layer, and a green tea infused foam base. 12 inches total. |
| Cooling | A gel memory foam layer works with the Hyper Cool cover's phase-changing material to pull heat away from the surface, keeping a firm all-foam bed cooler than older foam builds. |
| Motion isolation | Excellent. The all-foam build with no coils absorbs movement before it reaches the other side of the bed, so you don't feel a partner shift. |
Frequently asked questions
How firm is the Sierra Sleep Millennium 2.0?
Genuinely firm, this is a mattress built to hold you up rather than let you sink in. A thin gel memory foam layer softens the very top edge of pressure at the shoulders and hips, but the support underneath is firm from the first night, not something that breaks in soft over time.
Is the Millennium 2.0 memory foam or a hybrid?
All-foam, no coils. A gel memory foam comfort layer sits over a high-density support foam layer and a green tea infused foam base, 12 inches total. The firmness comes from a shallow comfort layer over a stable foam foundation, not springs.
Who should buy a firm mattress like this?
Back and stomach sleepers get the most benefit: firm support keeps the hips lifted and the spine level instead of letting the middle of the bed sag. Committed side sleepers usually prefer more cushioning at the shoulder, so ask the showroom team about a plusher option in the Sierra Sleep lineup if that is you.
Does the Millennium 2.0 sleep hot?
Cooler than a standard firm foam bed. The Hyper Cool cover uses a phase-changing material that pulls heat away from the body, and it works with the gel memory foam layer to keep the surface from trapping warmth the way older all-foam mattresses can.
Can I use it on an adjustable base?
Yes. The all-foam build flexes cleanly with a power base, so raising your head to read or your feet to take pressure off your back works the way it should. It also sits well flat on a platform or a solid foundation.
How long does it take to expand after unboxing?
Give it up to 48 hours. The Millennium 2.0 ships compressed in a box to keep delivery simple, and it needs that time to fully expand and reach its true firm feel before you judge it.
Does Sierra Sleep offer an at-home trial on this mattress?
No. Sierra Sleep mattresses, including the Millennium 2.0, do not include an at-home trial. Firmness is one of the easiest things to misjudge from a description, so the way to know if this is your feel is to lie on it before you buy, in your own sleep position, at one of our Kentucky showrooms.
Can I see this mattress in person near me?
Yes, and with a firm mattress that is especially worth doing. Mattress Overstock is a Kentucky-owned company with showrooms in Lexington, Georgetown, Somerset, London, and Richmond. Come lie on the Millennium 2.0 in your own sleeping position, and since 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.
