Sorry to hear about your scuba issues, that's tough. In the hotel zone Cancun, there would be few resorts where snorkeling would be good right at the resort. Down on the Riviera Maya, there are a few though. I could be wrong but that has been my experience. The Boobs Cruise you may read about on this forum stops for some snorkeling out towards Isla Mujeres and other excursions are available.