I know it sounds like you're not looking for a whole new one, but I'll through this out to you anyway.
We tossed our mushy spring mattress that came with and put in our 4" latex one from the house. Yes, only 4". And real 100% Latex. Not "Made with 100% Latex (that just means it has some degrees of 100% Latex added to the total). And we haven't got it on a box spring in the house either. It's awesome. They come in different densities. Heavier then a spring, can be rolled and tied and carried by myself. 1" blue foam board underneath to stay warm (huge difference!)
Some come with a cover but that could be opened for any trimming needed.
IMHO, memory foam is just foam that leaves a ditch for your bed mate to roll into and you to get stuck in. And thanks to a certain State, a lot of foam is really bad these days.
At 260lbs, the 4" Latex, in a firm density, is all I need. Love it!