I would suggest you check out Aquatic Sports.One of the oldest ops in Cozumel owned by a great guy named Sergio Sandaval.He has 2 boats that probably would be perfect.No rush outfit and they feed you a great lunch during surface interval.
I second the vote for Aquatic Sports, and also recommend Sergio's son Sergio Jr. (Aquatic Sports & Expeditions) I was out on his boat in April and there was a paraplegic onboard. They had no issue at all accommodating him, plenty of space on the boat, very impressive!