I trained in karate for a number of years, though never got my shodan (2nd kyu). I have also boxed on and off over the years.
Having got sober, I'm now looking to train again. I have thought about judo, but I really don't want to damage my back or knees, which the OP states is highly likely. I think BJJ is overrated and wouldn't be very practical in a street fight. Ideally I'd like to train in something I could continue into old age - so I'm considering wing chun. During lockdown I have been training with a friend, hitting pads, and practising some kicks and I'm enjoying myself. So I thought I might continue with that, too. We have been watching videos on YouTube and taking a good technique and then drilling it.
Has anyone heard of Russell Stutely and his wave form technique? I bought a copy of one of his books, and have watched some videos of his, but I can't quite seem to make it work. I think, in part, it;s because I have drilled conventional punches so hard over the years, that it's difficult to learn new habits.
Also my wing chun chain punches are really weak. I have seen demos of them, and know they can be quite powerful. I had a friend who was a football casual (hooligan) and one of the lads in his firm practised wing chun and apparently knocked a guy out with a single 'rabbit punch' as my pal described it.
Don;t get me wrong, I'm not at all violent. In fact I have let a few people off over the years, when I could have rightly battered them.