What I did was take some fleece I had (got it from the remnant bin at Joann's). I cut it in to strips. Mine were 3in x 11in but you could make them any size you like. That's it! Fleece doesn't unravel, so you don't have to hem them or anything like that. Very easy and so great for my little girl's butt. I've been using mine now for about 2 months.
I decided to use my serger and make some double layered ones too.