Most horses will click in a joint, it does not necessarily mean that they are arthritic.
Msm is a good idea, I feed it to all horses as a preventative measure, you can also add some glucosamine if you are really concerned which is good for long term protection of joints if fed on a regular basis.
Work boots won't do much at all and if you're not doing a hell of a lot of difficult work with him, they're not hugely necessary. I only boot my dressage horses as they are doing lateral work and collection places increased strain on their tendons. But they won't do anything for arthritis.
The only boots that might help are magnetic boots, I didn't see any improvement after using them on my boy with arthritis in his hock, but friends swear by them for their horses with mild arthritic changes so they might be worth looking into.
I, like tiny, would not bother with bell boots unless he is actually pulling front shoes off or damaging the coronet band. Otherwise, its just something else for him to trip on.
Again as tiny said, in most cases tripping is not due to arthritis and other medical reasons, but because the horse is not picking its feet up - being lazy. Do some work on getting him off your leg and moving forward without dragging his feet, lots of transitions and changes of rein. This will help him out on trails and well as any arena work.