my cat has dodgy knee caps now :(

[Tulips]

I don't know about cats but my dog had luxating patella, I went through with the surgeries in the first few years of his life and they have improved his life dramatically and have ensured that his knees won't trouble him excessively ever again.
I also give him supplements daily and take him in to the vet every 6 months for anti-arthritic injections, so I definitely recommend supplements and keeping a close eye on whether he is experiencing or hiding any pain and consulting your vets about all your options.

Did the vet tell you what levels (1-4) his kneecaps were at? I hope you and your cats stay well, and good luck limited jumping (it's a pain alright)