AirPods Pro: I have found an eartip with „good fit“ according to ear fit test, but only for one ear. For the other ear none of the three sizes seems to fit.

You can always check into ear hooks. I used them for a bit and the worked will. Could get a little tight from the pressure at times. Otherwise a cool trick I learned was to grab the top of your ear and pull it back a bit while putting in the AirPod. When you release the ear the ear holds onto the AirPod a bit more snug. Also, keep your AirPods clean. Any wax or oil from your skin on the outside of the ear cushions makes them harder to keep in. Keeping them clean makes them stick to your skin a bit more. Use a gentle solvent with alcohol like hand sanitizer and a tissue to gently clean the ear cushions after removing them from the AirPods. I’d say between that and ear hooks you’d be set. Oh and if you go the ear hook route get a few of the same ones. They don’t fit in the charging case so you’ve got to haul them along throughout the day separately. You’ll end up losing or tearing the silicone on some without question.