Doll-fins,
First,welcome to the board, from NJ, and congratulations on the OW!
The folks you have talked to have it right -Cozumel is a terrific place to dive-and not very expensive. In fact, compared to some of the other major dive locations, it is cheap!. I have been there three times-and I love it. There are other folks on this board who share that opinion-but I'm pretty sure that they will let you know.
A few comments regarding the diving:
First: many dives are drift dives, which require the typical attention to buoyancy skills.
Second: many of the dives are boat dives which, in my opinion, makes things easier.
Third: the vis is super!
Finally: On each of my trips to Cozumel, I have seen new divers do quite well.
I think if you are looking to dive in Mexico, that Coz is the place.
Let us know what you decide.
Good luck, and enjoy the board.
MikeD