Good RV Mattress for heavier people

We're in the market for a new RV mattress. We've lived with the original factory cheapo mattress long enough. Now, DW has suffered a fracture to her back and it is causing difficulty in her sleep, so the search begins. Our mattress is a standard 60"X80" mattress size. We are hoping to receive input on a decent quality, affordable and comfy mattress that will not crush through and leave us laying onto the plywood foundation. (BTW, we are not 110 pound teenagers) Any guidance and/or recommendations would be greatly appreciated.