Supplement wise, fish oil is good, but you should also look into making homemade broths (what many call bone broth). It's pretty easy. Some supermarkets have bones, but any butcher will be able to provide (discuss incase they need a little advance notice). I just made a batch with a mix of beef, lamb, and pork. I brown them up in a pan quickly (some people roast them at 400-425 for 30-40 minutes). Throw them into a pressure cooker with the fond, throw in some vegetables (you may want to add these halfway through), bay leaves, and garlic, then top off with a few quarts of water and let it cook 16-48 hours. I went 24 hours on low, occasionally skimming any scum off the top.
What happens is this allows a lot of nutrients/proteins in the bones to seep out, namely collagen, which is incredible for many parts of your body, including the digestive system, skin, hair, and joints/bones/tendons. It comes from the cartilage and marrow in the bones. Drink this regularly. Making a lot you can store them in mason jars too and freeze them (leave room at top for expansion) and defrost them as needed.
When you refrigerate, the fat will rise to the top and separate, making it easy to skim off, and the broth takes on the consistency of jello thanks to all the collagen. Just throw some in a pot and heat it up.
I find myself drinking a cup of it a few times a week out of a coffee mug. I just salt it a little since I don't season it while making it.
I suffer from bursitis in my knees after a car accident and some days my knees can really bother me, overall I've noticed I do feel a bit better, but your best bet as stated is to lose some extra weight, as every pound lost is a 4 pound reduction in pressure on the knees. In turn, the bone broth is healthy and filling too, and can help aid your weight lose by becoming part of your meals or a replacement for snacks.
Good luck with it man.