I can recommend diving in and around Chamela bay,(Perula). West coast of MX about 100 miles south of PV The diving is much better in the summer but is good year round. There is a dive shop in the town and the owner is well versed in all of the dive sites in the local area. He rents gear to certified divers and will provide guided dives or arrange for transportation do dive sites if you need assistance. Google Perula and check out some of the photos of the area.
I'd recommend bringing Masks ,Fins, Snorkels, and rash guards and leaving the tanks etc. at home. The coldest water temp last winter was a freezing 78 degrees f.