Hi Dynasty,
Welcome to the board!!!
I stayed at Aventura Spa Palace last year in late May. Beautiful place, you should be equally as pampered at Xpu-Ha.

Palace resorts have AquaWorld on site. You could arrange diving directly through them. They would make all of the arrangements to get you from Xpu-Ha to the dive site, including lunch. This is how I made my first dives (not just in Coz but first period

). If you do choose this way, ask for Enrique, he is an instructor/DM and did a marvelous job with me. My instructor at the resort had requested him specifically for me. At the time, I didn't know the difference between a good DM and a bad one. I do now. He's in the really good category.
So if you like to be taken care of, not have to worry about your own logistics, and don't mind a large dive op, they are there. While they may be referred to as cattle boats, I did my dives in a group of four, including the instructor, so I was a bit spoiled. Not sure what your choice of dive sites would be, since I only did those first two dives with them. ANYWHERE was good with me.
If you're more adventuresome, you can arrange your own transportation up to Playa del Carmen. (Gordon, ggunn, would be great for that advice

) And take the ferry over on your own. I'm biased as hell on the dive ops in Coz, and I do not have the experience to be that biased.

I love Christi and her op Blue XT Sea. She runs a very nice op. It's a great combination between serious diving and being pampered, I had thought the two were mutually exclusive, boy was I wrong. I've found a good thing, diving with BXTS, and I don't intend to mess with it.
Others here on the board can run down quite a few other excellent dive ops for you. But it really comes down to what type of diving do you want to do? And how much hand holding do you want, both above and below water?
Hope I helped. Now I'm going diving.........:lilbunny: