Since one of us has a hip replacement, and one of us had a broken foot, we are currently quite aware of falling risks in a wet tub.
We saw these bathtub Stickers online and decided they were cool. Easy to use. Make sure tub is dry. Remove paper backing. I had to bend over a corner to get the backing to peel.
Then, gently remove paper and press into place where it's likely that your foot will rest.
Do not use tub for 24 hours to allow adhesive to merge with your tub.