I do have a knotty shag looking bath mat, but it gets hung over the side of the tub after each shower and thrown in the wash with towels every week.

I used to have towel ones but a little cushion is better.

I primarily look for no backing . While non-slip is certainly important, I prioritize something flexible enough to hang over the edge of the tub and that can be washed frequently without falling apart. I’m not sure what athletics people get up to that need the rubber backing anyway