I use white plastic soft vinyl shelf liner that comes on I believe it is a 24 inch wide roll. It is like the spongy nonskid shelf liner with the square holes in it used to keep dishes from sliding around. It felt a little weird standing on it at first, but I got used to it and stopped noticing it. I cut mine about 24 x 16 or 18.
The only problem was that although being solid vinyl and it does not soak up water, water did get trapped under it, so I had to hang it to drip dry or stuff would start growing under it. When it does need cleaning I lay it in the tub and scrub it with a soft bristled brush with a little Dawn or clean it with Soft Scub with Bleach when I clean the tub and walls.