We want to get a different mattress too. I think it is a "standard" odd shape that is used in the smaller Class C's with no slide outs. The bottom comes off the bathroom wall at the bathroom door at about 45 degrees than meets the refrigerator wall and squares off to the passenger side wall. If it was square it would jut out and block the bathroom door so they cut that corner off. We got 3 years out of it but I really want to change it out. Probably have to have one custom made..
Apparently this mattress is a "bottom right hand cut corner" mattress.
I found a company named: FineWebStores.com out of Ohio that offers custom mattresses. They have measurement boxes that you fill out with your measurements and various style mattress components to choose from. No idea about this firm but I'm going to check out. Sounds like this is what I need.. We'll see.