Rickochet "Dead" feeling shaft is better than pain and/or no golf, right? Seems like a good problem to have versus chronic pain.
I'd go vibration dampening inserts first to see if you can get on with your existing grips, only because changing the grip would seem to have a more significant impact in your performance. The club will feel a lot different, release will change a little, etc. If that wasn't enough, then definitely try the big shock absorbing grips. The cost of that versus the cost of giving up something you really enjoy? Come on. Graphite shafts too. Expensive, but a small price to pay for being able to keep playing.
As for treating the arthritis, I don't have a lot of expertise. Supplements are available, but for general health stay hydrated and maybe consider a thumb splint to really rest your hands/thumbs when not playing. I had a very bothersome thumb sprain that curtailed my golf for almost a year - I finally got a wrist/thumb splint from Walmart for ~$15 that really aided in the resting/healing process.
Baby it as much and as often as you can when you don't need it. That'll give you as much usable life as possible on the course, hopefully.