First off, i am sorry you are dealing with chronic pain.
Indica strains are usually recommended for pain and sleep. They also are usually shorter then sativa strains.
Hashberry is a good kinda short one. It isn't a heavy hitter like Larry OG, but he can get big if not well trained. Look at Hamster Lewis' grows. He trains them and keeps them manageable.
I have read that blueberry is good for pain but I have no personal experience. I think all pot helps with pain, but some are better then others perhaps.