Throw some straw on a concrete floor and let him sleep like any other livestock.

You either buy shitty mattresses or your idea of a destroyed mattress is a lot stricter than mine. I’ve been that size for some time and am finally getting a handle on my health and I haven’t destroyed a mattress like that. That or he almost actively destroys them, like through lack of care or being a very restless sleeper.

Roll him over from time to time

most mattresses have a 250 to 350 lb limit total for the entire mattresses but they do have heavy duty mattresses out now that can take up to 800 lb

Get 2 twin mattresses. Your side will stay nice and he can destroy his

You may be buying cheap mattresses. I've been heavier than that, have been around that for a number of years now, and have never destroyed a mattress. I think I've had my current mattress for 5 years or so, and only replaced the one before that because I got an adjustable bed.