I've tested America's firmest mattresses — this is the one I'd buy in the Labor Day sales

(Image credit: Future) When you're a stomach sleeper, you get used to starting the day with back pain. I used to spend a good few minutes each morning trying to ease life back into my hips. Then I discovered the Plank Firm mattress, 30% off at Plank this Labor Day, and now I know what it's like to wake up feeling fresh.The Plank Firm is unusual. When it comes to construction and quality, it can rival the best mattresses we've tested. However, this double-sided bed is super firm and incredibly flat. That's heavenly for stomach sleepers (and many back sleepers) but it's not a feel everyone will enjoy.Where the Plank Firm excels is full-body support, and I'll explain below why that's so important for stomach sleepers. But if you're after something a little softer, check out the deals in our Labor Day mattress sales hub.Why the Plank Firm is my favorite mattress for stomach sleepersStomach sleepers, there may not be many of us but we know there's nothing more comfortable than burrowing into your bed face first. However, stomach sleeping does come with a (fairly major) downside. It's hell on your back.The best firm mattresses help offset that problem. On a softer bed, stomach sleepers will often find their body sinks at the hips. This puts strain on your muscles, as they work overtime to keep your spine aloft. (Image credit: Future)But firm beds hold the spine straight. By maintaining natural alignment, your body can relax and you'll wake up feeling fresh. For that reason, most of the best mattresses for stomach sleepers are firm.It's not just stomach sleepers who can benefit from a firm mattress. Back sleepers often need extra support at the spine, while even some side sleepers (particularly those with a heavier build) can appreciate firm support.And when it comes to firm, even support, no mattress has impressed me like the Plank Firm.Well. Maybe these two came close...More firm mattresses I've tried and lovedLabor Day mattress sales 2026: More deals at a glanceSaatva Classic – best overall: From $1,049 (was $1,449) at SaatvaZinus Green Tea Memory Foam Mattress – dorm room savior: From $173 at AmazonHelix Midnight Luxe – best for side sleepers: From $1,119 (was $1,492) at HelixDreamCloud Classic – best value: From $429 (was $1,346) at DreamCloudBear Elite Hybrid – best cooling: From $1,298 (was $1,998.80) with TOMS40 code at BearBrooklyn Bedding Copperflex Pro – best value cooling: From $652 (was $932) at Brooklyn BeddingTempur-Pedic Tempur Cloud and smart base – best bundle deal: From $1,718.40 (was $2,598) at Tempur-PedicAvocado Green – best organic: From $1,279 (was $1,599) at AvocadoPurple Plus - best for joint pain relief: From $1,280 (was $1,599) at Purple Follow Tom's Guide on Google News and add us as a preferred source to get our up-to-date news, analysis, and reviews in your feeds. Get instant access to breaking news, the hottest reviews, great deals and helpful tips. Ruth is an experienced Senior Staff writer at Tom’s Guide, covering all things sleep and mattresses. She writes to help people sleep better, from how-tos to the latest deals to mattress reviews, and has interviewed an array of experts who share her passion. She is also our specialist on memory foam — she’s flown around the world to see memory foam being made — and leads our hotel mattress content. She has a deep interest in the link between sleep and health, and has tried enough mattresses, from Helix to Nectar to Simba, to know the right bed really can make a difference to your wellbeing. Before joining the team at Tom’s Guide, Ruth worked as a sleep and mattress writer for our sister website, TechRadar.