Nudity is acceptable at one end of the beach. However, in my expericence few people choose to go nude and those that do are mainly Mexicans.

Never saw a bongo playing idiot there.

Definitely look into Tulum. I can´t think of another beach town that compares in all of Mexico. Try doing a websearch and see what you like from the results.

Sayulita sounds like your kind of place, just north of Puerto Vallarta, you can take the bus to it from PV or take a cab, no need for a car. There are many inexpensive places, it is small and less hectic than PV. A nice clean place in town is Bungalows de los Arbolitos