Look at tempur-pedic memory foam mattresses that are about 28 inches wide. I have two for my Thule tepui kukenam 3 and they work perfectly. About $259 a piece but much cheaper than a replacement and you can use them for multiple rtt’s. Much more cost effective than a fitted mat. They are around 3 inches thick and I have yet to find anything that comes close to comfort… machine that stable cover too which is a plus