We bought a
10" Zinus Green Tea Memory Foam mattress from Amazon. You get a 30 day warranty and, while I have not tested the process, was told they have contracts to have them picked up for return if requested.
We've slept on it and it's far more comfortable than the factory mattress. DW likes it a bit more than I do but it's a huge improvement. By replacing it you lose the heated mattress part but you can replace that with a heated mattress pad. As we're going to dump the factory mattress I'm considering taking the top liner off to see if I can salvage the heater somehow.
Note: ours is a full queen, not RV queen. I don't know if the foam around the edges differs from the foam in the center but, if length is an issue, perhaps you could cut a few inches off the end if you can't find an RV-specific size. If you do, use a bread knife.
After a second trip we determined that it being 10" interferes with the headboard when opening the bed. You have to pull the mattress toward the foot of the bed to get it past the top corner of the mattress. It can drop back to the normal location when fully opened.
We ordered the
8" version of the same mattress as a replacement. We tried the 8" at home and find there is no difference to us. We're leaving on a 2 week trip soon and will know for sure.
For reasons I don't understand, the 8" costs $10 more than the 10". The 6" is much cheaper than both but I'd think the difference in padding would be significant.