Freejump and flex-on I believe could help
Here is a website and the irons I would recommend any flexi ones are good for joint stiffness and pain and these arnt a ridiculous price either
Hope this helps
Maybe plastic ones? I also know if an exercise to help!
When Im riding my horse, I take my feet out of the stirrups and roll them between walk breaks. I recently tore my ligaments in my left ankle and it really seems to help! 😁 😊