I love Cenote TTDs! They are unique to this area and are just magical. If you are planning on being underwater, there will be shots where you want your eyes open, then contacts would not work. Perhaps you could have your glasses and contact case with you and switch out if needed. Also, due to the sediments in the Cenotes, I would recommend using 1-Days for that shoot. As a local scuba diver (and very blind.. hehe), I always where 1-Days when diving to avoid accumulating bacteria on my contacts.
As for dresses, definitely something that can billow out a little and NO materials that will become waterlogged and difficult to swim in!
Lori's Office Assistant