I believe it wasn't too long ago when CarlyBaby's precious little Beatrice jumped off the couch and broke her leg needing surgery as a result.
Even if nothing happens now, in the long run, the stress on his knees will more than likely result in leg surgery, provided he doesn't seriously hurt herself any other way first.
Doggy stairs would be best and hope he uses them. I'd be worried that he wouldn't be able to land properly and/or safely all of the time.