Probably a kitchen cotton, the kind you'd use for dishcloths. Held singly or doubled, but you may want to put some sort of nonskid backing, though a lot of those woven kitchen rugs don't have that and they're not that skiddy.
Rug yarn is designed for this. It used to be available at all the craft stores in the 1970's. Man, you can tell I'm old. I don't see it around so much anymore. You may be able to order it online. The most popular one was Aunt Lydia's Rug Yarn.