Sounds like you need a resort on Cozumel or Playa Del Carmen. I just don’t know of any to recommend. I always do the same family vacation in Cancun, and use the off site dive operators 10 minutes drive. I’m back by lunch time. But there is no on-site snorkeling. The closest snorkeling is a ferry ride away at Isla Mujeres. I’m sure someone will have some Cozumel suggestions soon. I will be interested to see any suggestions as this is a goal for me as well.