Velcro Tape (US link. I got a different one, but the VELCRO brand one made specifically textiles should stick on even better. If they eventually fall off, use Gorilla textile glue to hold them on permanently)

This adhesive velcro tape is my alternative solution for keeping a sleeping pad from sliding around in the tent. Put a few pieces on the tent floor and the pad and it works like a charm—same idea also works for attaching a pillow to a pad.