We just came back from Destiny on May 18th. I think you'll love the Playa Mia Beach Break in Cozumel. We did the train and trolley tour. As for Key West, see if you can take a taxi or something to get to Hibb's beach next to Casa Marina Resort and Beach House. I took some pictures and this is a public beach and it looks like you can rent whatever you need there such as umbrellas and kayaks. If my husband and me go back to Key West, this is where we will be spending the day. Since we missed Cozumel because of the flu thing, we got to stay in Key West until 4:30 pm. It was awesome to have that much time there before our day at sea and stop in Nassau. If your port stop is only 7am to 2pm. I would suggest going to the Southernmost Cafe and Beach. The water is baylike but it's a nice little place to get some sun, a reasonable lunch and a drink. They have lounge chars, umbrellas and palm trees... Have a great trip!