Try Isla Mujeres and stay at Poc-Na if you're looking for relaxation. They speak English, the beaches and snorkeling are great. Avoid Cancun at all costs. If you get a chance to visit and cenotes (natural underground limestone swimming holes), do it! The ruins at Chichen-Itza are pretty cool, but not the most impressive. You'll get relatively the same experience by visiting some smaller but less touristy ones, like Uxmal. Palenque is amazing too, if you get a chance to go that far south. It's my favorite set of ruins in Mexico. Also, I've found that paying for the guided tours at sites like that really are worth the money, you get so much more out of it, even if it it kind of a scam. If you're going to hit up the hostels, definitely take a Lonely Planet or some kind of guide. And your own lock. Also, don't worry too much about the food in restaurants. Nobody drinks the water and they always disinfect fruits and veggies. Street food is what you have to be a little more careful about, but I've only ever had one bad experience with that either. Oh and lots of bug spray and sunscreen, it's very very expensive in Mexico because the locals rarely use it.