We had the same problem in our Lexington and looked up local mattress manufacturers and low and behold, there was one in our area. They made a great mattress and in speaking with the couple, they did a lot of motorhomes. We had to take the motorhome to them so they could measure properly and they made one that was flippable (many today are not). We sold the Lex and the mattress went with it. We like the one in our new Aspect, but if we get to the point of needing something else, we know where to look.
Look up manufacturers in the yellow pages...or google it