Looking for inexpensive upgrade for bunk mattresses....

I also recommend trying to buy as big of one as you can with the hopes of cutting it and fitting both beds. Should be able to measure the two to determine if you are able to do that. Memory foam is very easy to cut with an electric carving knife. I recently cut a king down to fit an RV king with rounded corners, took longer to take the matteres out than it did to cut the memory foam. Good luck and happy camping!