I found thin rubber band in a craft supply shop and thought it might be good for doll shoes. As it's stretchy, you don't need buckles in straps.
I had a short piece of cardwoven band and I thought I wouldn't have any use for it as there was so little. However, there was enough for the vertical parts into which I glued the rubber band straps.
This photo shows how the straps were glued. First, I put glue to the underside of the vertical pieces, then placed the straps in place and let dry. When the glue was dry, I spread another layer of it on top of the straps to make sure they will stay in place. As this side won't show, it doesn't matter how it looks like.
Then I glued the ends of the straps under the insoles. I placed the insole against the doll's foot, placed the piece with straps in correct position on top of the foot and then glued the ends under the sole so that it was a tight fit, but without stretching the rubber bands.
Here is a picture of the finished shoes. The heels are made of balsa wood covered with leather.