My wife and I been to Cozumel 3 times and loved it, Senior Frogs is great. We took a flight to Chetchen Itza, about 45 minute rather than the boat and bus, well worth doing. I would rent a jeep, you can circle the Island in 45 minutes.
Great diving you’ll have awonderful time. They do siesta from 2pm to 4pm not much going on in town at that time.