When I slept on the Plank Firm mattress, now from $524 in the Plank 30% off 4th of July sale, I was most impressed by the full-body support. From my shoulders and lower back to my and hips and toes, my body was lifted and straightened, helping undo some of the tension from hunching over my desk all day.
The Plank is a slightly unusual mattress. Actually, it's very unusual. Not only is it a firm all-foam bed, it's also double-sided, meaning you can flip between Firm and Extra Firm feels. While the best mattresses we've tested tend to be crowd pleasers, the Plank is targeted at a specific audience: those who want a harder mattress that feels like its straightening out their spine.
If you're looking for a firm bed in today's 4th of July mattress sales, I don't think you'll find a better option than the Plank (especially as its back to its cheapest price of the year). Here's why...
Excellent support to ease back pain
I'd describe the Plank Firm's support as 'unyielding.' That might not sound like a compliment at first but it describes how the Plank Firm is able to hold my body in a completely straight line from head-to-toe. It's this feature that earned it the title of the best firm mattress of 2026.
Unyielding support means there's no sagging, sinking, or dipping that might put unwelcome strain on parts of the spine. Because my body doesn't have to work to hold itself up, it can get on with what sleep is meant for: rest and repair.
Ideal for back and stomach sleepers
While side sleepers tend to benefit from a softer bed (you'll find our top picks in our best mattress for side sleepers guide), back and stomach sleepers often need something firmer.
When you lie on your back or front on a softer bed, your hips tend to sink lower than the rest of your body. This puts pressure on the spine and can cause long-term discomfort.
But a firm bed, like the Plank mattress, keeps those hips lifted. It's particularly good for stomach sleepers (our best stomach sleeper mattress guide is dominated by firm beds). Stomach sleeping already puts your spine in odd positions — you don't want your mattress to make it worse.
Strong from edge-to-edge
Edge support refers to how sturdy a mattress is at the perimeter. Strong edges allow you to stretch out and make it easier to climb in and out of bed. Firm mattresses don't always have good edge support but the two do tend to go hand in hand (when there's less sink in general, the edges are less likely to collapse).
The Plank Firm has exceptional edge support. I always sit on the side of the bed while getting my bearings in the morning and on the Plank, I could believe I was sitting on a chair. These are sides you can park a truck on.
More firm mattress sales to browse today...
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