Dri-Dek, if your feet can handle the nubs. Mine can't. It's used in public shower areas and allows water to freely flow to the drain. It's available at Home Depot and the like.
I use an old towel folded in the shower. Warm on the tootsies during those nighttime excursions. Easy to take out and shake. Place outside the door when showering, instant shower mat! Hang outside to dry.
YMMV