.......Right now, I am thinking maybe of starting at Puerto Morelos or Playa Del Carmen for a couple days and then maybe over to Cozumel. Cozumel seems to be coming highly recommended by many, but maybe with a tad bit more diving experience.......
When diving Cozumel this time of year, you have to factor in the "nortes". ("norte" is spanish for "north", and it's the term for the big winter cold fronts, that are the exact same ones that are hitting the states at the same time).
When these fronts come in, they bring lots of wind, that churns up the water, often resulting in closed ports, and either no boat diving is allowed, or only larger boats can go out (which still sucks, for several reasons: The boat trip is cold,windy and turbulent, and all the dive operations frantically try to book the few large boats, which can result in different groups from different shops, all over-crammed onto one old, slow,boat that wasn't designed to be a dive boat, and isn't well suited for extra-large groups of divers. ).
And it isn't just the leading edge of these fronts that wrecks everything, it'll be the several days of wind that follows it.
Cozumel's western shore (where all the good diving takes place) is facing NW, so it takes the brunt of these storms, while Playa Del Carmen,etc. are on the lee side of the Yucatan land mass, and can often be much calmer, especially close to shore (where, unfortunately, there's pretty much nothing to see, but you could at least get in those refresher dives).
Most of Cancun's dive spots are out in the ocean off the north point, so they're still in the middle of it (but cattleboat operations like AquaWorld have big boats that aren't affected by the port being closed, and they'll drag 20 friggin' resort divers out there, and toss 'em in the water ! They don't give
even a single a damn,LOL !!! ).
Anyway, the point is, closely check the weather, and even call the shop on Cozumel you plan to dive with (though if they don't have your money yet, they'll tell you everything's swell, come on over !!!) But, if you understand this weather pattern and it's effect, you can easily make you own predictions.
I haven't looked at the weather-sat lately, but I'd be willing to bet this nasty front we've been dealing with here in the US, is making life miserable for divers down in Cozumel right now, and will be for a little while.
edit: unless you're dodging bad weather, i wouldn't waste a nickel diving Playa or Morelos. If you're certified, you have plenty experience for diving Cozumel. Nervous,inexperienced divers are their bread and butter ! You'll be fine!