I made mine over 15 years ago, I still have it and use it for "camping out."
I went to the fabrick store and got some nice cooshy 1 inch thick foam, then a ugly but soft knit material taht was on sale to cover it with, I made long "straps" on one end so I could roll it up and tie it tight at the end. Was much more comfortable than the ones my friends bought for the class.
Try calling sports stores, or even, if I remember correctly, you are on the petite size, look for a "nap mat" for a young person (like htey would take to day care), they are usually 4 of 5 foot long... that is waht a bunch of the people in the class got also(or 2 to make it long enough)..please remember, this was about 15 years ago.
GOOD LUCK!