My son went last summer with a group. According to all the research we did (although I HATE tours myself, except when in a country that requires them for safety sake) this is a place you'd probably want to tour with a guide or group if possible.
He did the rainforest canopy tour and loved it and they did have some time for beaches and shopping. Watch for pick pockets in shopping areas. They can pick Americans out easily!
"Life is a lesson in humility"