I'm so sorry that you are going through this and with such a young puppy at that. Though his age may be an advantage in a way, perhaps the ortho vet will have more options for him since he's not so likely to have arthritis in the joints yet. I want to second (or third) the suggestion for gluc/chond/MSM supplement. We've been using it for years for our dogs and it works wonders at helping give them comfort and better range of motion. My parents have given their sweet old mixed breed dog another 5 yrs or more of happy life by giving her this supplement. They were told when she was 10 y/o or so that they would have to put her to sleep due to severe arthritis pain, but she's 15 now and doing still doing well with the supplement and a mild pain reliever given by the vet.
There is a lot that you can do for your pup. Between the vet's recommendation s, supplements, changes to your lifestyle (no stairs, jumping, etc.) I'm sure that you'll be able to help him. Please give him a kiss for me and let us know how it goes.