After trying a couple of makes, I found the "Goldilocks" of yoga mats that works perfectly as a pin cover (not too thin, not too thick, not too much memory to stay rolled up):
Only £8.95 on Amazon - trimmed top and bottom edges first for length with a Stanley knife, then down the side using the glass to get it nice and straight:
Only £8.95 on Amazon - trimmed top and bottom edges first for length with a Stanley knife, then down the side using the glass to get it nice and straight: