Adequan injections are often helpful and can be combined with oral glucosamine/chondroitin and MSM. They help with cartilage repair and joint lubrication. Omega3 fatty acids are another option and have natural anti-inflammatory properties. Glyco-flex (contains green-lipped mussel, an excellent source of fatty acids and chondroitin) is something I've been using on my very arthritic kitty, along with Cosequin and osteopathy sessions. Acupuncture would also be worth looking into.
Pet beds with egg-carton foam or memory foam help with overall comfort, and my cat absolutely loves his heated bed.
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler