Mattresses for fat people

My boyfriend and I are fat (me 240lb, him almost 400lb). We bought a king Purple mattress a little over two years ago and his side of the mattress is ripping down to the springs where he sits up on the side of the bed in the morning/gets into bed at night. I want recommendations for mattresses that are a good fit for heavier set people and built strong to withstand this kind of thing. This whole thing is so frustrating because the Purple mattress is so expensive. I’m worried that the spring will pop out and stab him because that exact thing happened to me in high school with a super old mattress. Please any and all recommendations or experiences would be greatly appreciated.