Mopan River Resort would be a nice launching point. It's in Benque de Viejo. We did Mayan ruins, cave tubing, river kayaking from there. It's all inclusive for meals, drinks and excursions. Just find out their typical trip schedule to see if they have the activities you want on the days you'll be there. You can easily google their website.
Get an A/C room (for daytime) while on the mainland! But I loved having the (screened) windows open at night. Very pleasant to hear the night sounds while drifting off to sleep : )
The birds and gardens are just gorgeous!!