Have you thought about maybe using flats pedals-with or without pins? I have to wonder how much difference there is between clipless and flats for those of us who are older or not trying to set speed records. Not trying to start a clipless vs flat debate (tho seems that happens sometimes). Did a little looking around and found this:
Are there any scientific studies proving the benefits of clipless pedal systems? - Bicycles Stack Exchange I'm a "recreational" rider, not too slow, and using flats with pins. Have no problem keeping my feet firmly planted on the pedal with them. Wish you the best and kudos for not letting your knees stop ya!