Firm and Medium-Firm mattresses are most suitable for back and stomach sleeping. If you sleep on your back or stomach, you'll want a mattress that's supportive enough for your body type, and firmer mattresses often provide better support, which helps keep your lumbar lifted and your spine in a straight line. You can also look for a responsive mattress with a bouncy feel, so it's easy to move around on, and good-quality foam layers, which make a mattress more durable. If you sleep hot, you'll also want a mattress that keeps you cool throughout the night. And if you sleep with a partner, look for an option with good motion isolation, so you can sleep peacefully, even when your partner tosses and turns.