@enduklee
IMO What to do in Cancun, if you want to explore the Yucatan, is to use it as an arrival and departure airport. If you choose the all inclusive resort option, most tourists do the expensive bus tours of the sights, many with emphasis on theme parks rather than cenotes.
NO availability in Tulum? Maybe right on the beach, in the cabanas, but in the pueblo (where we prefer to stay anyway)? Highly doubt it.
Puerto Morelos? Playa del Carmen? Akumal?
Ruins include Chichen Itza, Ek Balam (overnight in Valladolid), Coba (on the way to Tulum) and Tulum. Add Merida, and Uxmal, Rota Puuc sites, haciendas. Add Sian Ka'an biosphere from Tulum. Lots of cenotes.
Good plan can be a ruin in early morning and a cenote or beach in the afternoon.