I think it's a very personal decision, especially as you know your dog best so are best placed to know what makes him happy. But dogs are amazingly accepting of what we ask of them, so don't worry too much about making changes to his routine as time goes on. I think you may be pleasantly surprised at how he adapts. Then once those changes have become part of his routine he'll just get on with them.
To give an example, a friend's working Cocker has had horrendous joint problems since he was young. He's 11 now and a lot of his exercise has been on lead for many years but always with off lead spells at rabbit warrens. They are his favourite places and he gets so much mental stimulation and pleasure in 10 minutes of sniffing in rabbit holes that he's then very relaxed about being back on lead until the next rabbit warren. His owners work from home a lot, so I'm sure it helps that he has company most of the time, but he's a really happy dog and when they made the decision to limit his exercise, many years ago, he just adapted to it really quickly.
William is a year younger than Ben and was diagnosed with lumbosacral disc damage 5 years ago. He's still very active, although has never liked swimming, so that's one thing I don't have to worry about. I do some of the same things as you - no walking in hilly areas, keeping him slim, glucosamine and chondroitin etc. I also don't allow him upstairs and I tend to do most of our walking in one or two familiar places now, so he doesn't get too excited and charge about like a lunatic.
I've noticed he trots rather than runs if he has a tennis ball in his mouth so I encourage him to carry one (I don't throw it, just let him carry it) because it slows him down a bit. If he doesn't want to carry a tennis ball I put him back on lead for a few minutes every so often to slow him down. He didn't like it at first but has now accepted it as part of his routine. He likes rabbit warrens and he likes using his nose to find hidden treats so we sometimes stop at a rabbit warren for several minutes to keep him amused or play a couple of scent games. That all helps to keep his walks interesting without him overdoing things.
William also has acupuncture every 8 weeks or so. I was a bit sceptical at first but thought it was worth a try. The acupuncturist is a vet and during each session she tells me exactly what she's finding as she examines him and then sticks needles in him! It's fascinating for me because sometimes I will have noticed that he's been a bit stiff in a particular area and she always finds exactly that when she examines him and treats him. She also often finds other sore spots and treats them. William is noticeably more supple afterwards and I'm no longer sceptical. So it might be worth considering it for Ben.
I've just read lexi's post now, having typed my usual essay
and she's said pretty much what I wanted to but with fewer words!
