Wanted to add @tootrueblue Consider Yucatan as well. Really loved the combination of paradise and Mayan ruins. Tulum, chichen itza, Isla Mujeres.
The first week we stayed in a big resort in Riviera Maya , the stretch of coast between Cancun and Playa del Carmen, plenty of resorts, one after the other, but wouldn't recommend it as too much sea vegetation, it is like swimming in a sink filled with salad.
However further down, the beach and water is lovely we spent some days in Playa del Carmen and beach, city, night life was lovely. You go to dinner in a restaurant on the beach and the small bar next door has a band and everyone starts dancing on the beach.
We were not in a resort there, but a small hotel called Alhambra, they had yoga classes, ... not a resort but I am sure there are resorts there and you can do day excursions to the Mayan Ruins. At the Coba ruins, you can rent a bike , and cycle in the jungle until you reach the ruins.
There is an island called Cozumel in front of Playa del Carmen, but we didn't have the time to go. We were meant to take the ferry, but instead, had a lazy day in Playa del Carmen.
We concluded out trip in Isla Mujeres, a small island in front of Cancun. Gorgeous, but again there, we weren't in a resort.