I was down that way the 1st week of May. A full 3/2 was fine. Water temp ran 84-86F and cenotes were at 75F and was never cold. As for other protection, I put on some safe sea on both exposded and un-exposed areas including under the wetsuit. I had no problems but my buddy who did not use it and was wearing a 3/2 shortie was eaten alive by sea lice. After putting some on after the fact it seemed to reduce the bites dramatically. You may want to pick up a bottle for the trip.