Hello,
I dive Cozumel every year and use Dive With Martin they have the fastest boats on the island and there are no more than 8 on a boat you can dive your computer and there rates are fair. We stayed at Park Royal and walked a little over a block to the dive shop, they let you keep your gear there so you don’t have to carry it back and forth. As far as shore diving goes I don’t think there is a lot but there are a few sites Get back to me if you like and I can give you more info.
scubajoe