Mary, probably not. It is a full size 8 inch Gel Tempur Foam mattress. However, I purchased a 4" tempur topper and a 3" gel topper and cut them to fit my side dinette when made into a small (accent on small) single bed. I then purchased a nice mattress pad and sewed it into a "pouch" to encase the toppers. When not in use I roll it up and put it away. Very comfortable.
I found the name of the place that makes the custom mattresses for the Casitas. They may be able to come up with something also.