u/Comfortable_War5757 has some great suggestions for dealing with the feet that you should definitely try. However, since the foot-hip muscle chain is very interconnected, it's possible (even likely) that the PF is starting much higher up. How is the mobility in your hip following surgery? Can you walk naturally, or do you sort of shuffle or stumble along? Can you squat? (Yes, at 86 you should still be able to squat. You should be able to do it at 106.)
PF is also often aggravated by tight calf and hamstring muscles, which naturally follow when you have reduced mobility and sit down all the time. You could start by stretching those and working on getting as much range of motion as possible back into your hips.
Katy Bowman has a book directed at seniors called Dynamic Aging. It goes into some of the stuff I've just covered in much better detail, and also has specific information on how to adjust the exercises, etc for people with hip replacements and the like. Well worth a read.