You could consider contacting
Diablo Divers . . . Dennis Weeks, the owner, is a lovely man and a very good guide. And his partner, Natalie, is absolutely irresistible -- about 4'11" and cute, but she can stand up from the ground in a set of doubles! They're really nice people, very safety conscious, and truly love the caves.
Another good option, especially if you are staying in Coz, is
German Yanez. Also a lovely, gracious man, he is also a very experienced cave explorer, and an authority on the endemic species of the caves on Cozumel itself.
If you were going later in the year, I would recommend my very good friend Jason Renoux -- Jason's a delight, a beautiful diver and just a joyful person with whom to spend a day. But Jason's in Malta this summer.