Help Merlin run again

Merlin is a 2 year old labrador X golden retriever and safe to say he's my absolute world. Unfortunately when Merlin was only 10 months old he was diagnosed with patella luxation in both hind legs. He was too young at the time for surgery so we had to limit his exercise and go for hydrotherapy. I do have insurance for Merlin which covers 2k per condition. Merlin then had surgery 17 month which Unfortunately did not work. He had a second surgery back end of last year to try to correct the failed surgery as well as a torn cruciate which also has failed and has actually made the leg worse. He now needs referring to a specialist for both legs starting with the right which is going to be atleast 6k then correcting the left hopefully once recovered. My insurance will not up their limit and no other insurer will cover it. Any one that knows me knows how much this is breaking my heart, he's my baby. I've already used my savings on excess and I'm now stuck on what to do. I just need him to be a normal pup again without restrictions. He's currently on 3x 15 min on lead walks a day and that's it. Anything that anyone can donate I'd be forever grateful.

We have now had an appointment at Kentdale specialists vets where Merlin had a CT. Myself and the surgeon have decided it is best to start surgery on his non surgical leg as it will be far more straight forward. Merlin is now booked in for this surgery on 11th September. We have now raised £4500 for this leg so thank you so much to everyone that's donated! We still have a way to go for his left leg which is going to be far more complicated with already having hardware in it. I'm hoping it's not going to be anymore than the standard pricing but will find that out in due course.