Most ships allow you to take towels from the ships. just bring them back as they will charge you $20 per towel missing.
We did Snuba in Cozumel through snubacozumel.com. They have a desk at Chak. Park but also have a desk at the Cozumel Hotel and Resort. No crowd and helpful guides. Snuba is a kick.
We then went to Paradise Beach Club. A great place. Reviews on other threads on this board. Buy drinks/food and you can stay and play for free. Free snorkel, kayaks, water trampoline, floating rafts, beach chairs and umbrellas. Snorkelling isn't overwhelming as you are on a sand beach, though. Rent jet skiis next door.