Just in case nothing's been booked yet, a buddy of mine has a nice little Condo about 10 - 15 minutes walk from downtown (Senior Frogs, Carlos & Charlies, the Square etc.). Comfortable rooms, TV, air con, kitchen, showers, all the usual stuff you would expect. They also have a pool area for lazing with a cool beer at the end of a long day's diving.
When we're down there we dive with Caribbean Divers, a great bunch, always have a DM in the water but let you do your own thing or follow them, your call. Its often worth staying fairly close as they can spot critters that most of us would just glide over.
Anyway, if you're interested, I can get the details and put you in touch with the right folks.
By the way, love Cozumel diving, did the Devil's Throat for the first time a couple of months ago, a great dive!