Since you say "resort," you can't get much nicer than Hidden Beach. But it is pricey. A cheaper option would be to go to Azulik, which is next to a clothing optional beach. That's a little rustic for some, and it has a kind of youngish backpacker-honeymooner vibe. Or you could go to Intima Resort, which has a great pool, and then drive 15 min to the Biosphere (or 5 min to the Azulik beach). There's always Desire Pearl, if that's your scene. Or finally- though I don't think you could call it a resort- you could drive a couple more hours south to Xcalak and go to Playa Sonrisa. Great beach there.

All are good options- just slightly different, depending on what you're looking for.