For Cenotes, look at Cenote Xperience out of Playa. Hands down one of the best dive ops I've ever dove with. Depending on the time of year, Choc Mool is one of the most beautiful dives I have ever done.
For Cozumel, we like to dive with Aldora. ( 2-3 times a year for the last 5 years) With 4 divers, it will be just as cheap to charter your own boat so you can leave when you get off the ferry. Otherwise, their "normal" dive trips leave the downtown pier at 7:30. I believe there is a 6 am ferry from Playa.... it that would be a early day to make it.
Safe travels,
Jay