You can go alone and have a wonderful time. The people of this beautiful little island are very friendly and helpful. There are many excursions you can take also. In fact if you are there in September, you can go snorkelling with the whalesharks which is just truly awesome!. The food at the restaurants are great and most folks speak some English if you need help. You can travel the entire island in 3 hours with a golfcart lol Renting a tour would eliminate some of the best parts of this paradise. There are certain parts of this island that you may want to just stop and take in the scenery, or chat to the locals. Perhaps go snorkelling in Garaffon Reserve. Walk on the wild side,, it's very safe Dar
Isla Mujeres is my preferred Sunday escape. You can explore it on your own, shuttles leave every half an hour from different points in the hotel zone and Puerto Juarez. I recommend, breakfast restaurant Bucaneros, a few hours on the North beach, rent a parasol, then a walk through the markets and a light lunch mid afternoon.