Can a mattress support 400 lbs without breaking down

Look for high-density foam, at least 2.5 lb/ft³ or higher. Most mattresses use 1.8 lb foam which breaks down fast under heavy weight. Also check the warranty - some exclude weights over 300 lbs

I'm 350 and had good luck with a latex mattress. Dunlop latex is dense and doesn't sag like memory foam. It's not cheap though.

Honestly,at 400 lbs, you might need to adjust expectations. Most consumer mattresses aren't built for that long-term. A firm innerspring with dense foam might last 3-4 years, not 10.

I'm 280 and my foam mattress sagged in 18 months. Can't imagine 400. Following this thread.

Check out the Titan by Brooklyn Bedding. It's specifically made for heavier people and rated up to 1000 lbs. I've had mine for two years at 380 lbs and no sagging yet.

Titan is a good call. Also Big Fig is another one. They use high-density foam and rei nforced edges.

Second Big Fig. But note their warranty has a weight limit too, I think 500 lbs per person. Should be fine for you, though.

Side sleeper at 400 lbs - you need pressure relief. Titan might be too firm. Consider a soft latex topper over a firm base. That's what I did.

Toppers can help but tney also break down faster. Just factor in replacing the topper every year.

I'm a side sleeper and the Titan is fine for me. It softened up after a feew weeks. But everyone's different.

One more thing - make sure your bed frame has proper support. Slats no more than 3 inches apart. A weak frame will kill any mattress.