Welcome to the Board. You'll love Cozumel,as for suggestions....
Occidental Grand Cozumel, All Inclusive Mexico Resort
and for diving:
Welcome to Dive Palancar, Watersports Operator for The Occidental Hotels & Resorts Cozumel.
I can highly recommend The Grand Cozumel. It is an AI with very friendly staff, the rooms are very nice, the dive op is very good (make sure you get at least one dive with Ismael). My wife ands I go there every year