I have the Mombasa, and ended up ditching the matttres and picking up a medium density mattres. I like the added stiffness. I don't hit the bottom when I turn over. (185 LBS).
I like the mattress in my RTT but I too found them hard after a night or two. I have since simply tossed in my air mattress on top of the mattress. I use a 12volt inflator that has my queen size mattress up and ready in about 30sec. I feel I sleep very well and the cold doesn't seem to penetrate thru the original mattress. I also use an Adam and Eve queen-size zero-degree rated bag. I don't get cold anymore. But I stay out of the high country in the winter!
I added a 2 inch queen size "egg crate" foam mattress pad under the OEM mattress in our Series 3 Eezi-Awn 1600. It is overkill but I tend to do that with everything...
I got one of these. My mattress was firmer than I wanted and now its really comfortable. I don't camp that much in really cold weather so I don't have any idea how it does in those conditions. Have camped in sub freezing temps with a tent heater and it was fine.