I suggest that you experiment a bit with your memory foam. You have 2" foam, so double it over and take turns lying on the 4" of foam. How does it feel? If it's good, buy another 2" memory foam and lay it overtop the 2" you now have (lighter weight to roll them up separately, plus you already paid for one of them so why get rid of it?). If 4" of memory foam does not satisfy you, it's time to look for a different solution.
Possibility #1: an air mattress, either alone or with the 2" foam on top. Even a couple of those individual-size air cushions they sell for camping, laid side by side, might do the job under your existing foam.
Possibility #2: add some sort of cushioning fibers. The "Cuddle Ewe" topper is made of wool, do an internet search for it. Or experiment with some comforters or sleeping bags laid underneath the memory foam.
