Most flights go to Cancun. Cozumel has various direct flights, mostly from the US.
In Yucatan, the infrastructure is good with a few main highways (the rest is jungle) and ferry services between Playa and Cozumel. Taxis, tour operators offering day-trips and rental car agencies are everywhere, so getting around is easy (and not expensive).
There are hyperbaric chambers in the most popular cities/areas, including Cancun, Playa del Carmen, Cozumel and Tulum.