Hi Dalton! Cozumel is as safe as anywhere else, you just have to be aware, but that is true everywhere you go. There are tons of great things to do there, most revolve around the ocean, but there's also good shopping and tons of restaurants. The ruins are fabulous, too.
I'm not sure if you enjoy snorkeling or diving, but Belize is fabulous for both. The reef you go to there is second only to the great barrier reef. It goes down to Honduras (Roatan), too. If that's one of your destinations. I've not been to Belize City in a long time, mainly because I've done some great snorkeling excursions and haven't had the time to go into the city. My co-worker loves going into the city for shopping, eating, and drinking. Then he goes to a private island, I'll ask him the name if it interests you.
Hope you have a marvelous cruise!