If you're looking for thatch cabanas on Ambergris Caye, your choices are:
Hotel del Rio
Victoria House (some units)
Xanadu (not your traditional thatch construction, though!)
Hope I didn't overlook any.
A few other places such as Capricorn have cabins/casitas (not thatch).
Personally, I think the cabins and cabanas are over-rated. Give me a beautiful new reinforced concrete villa or condo anyday. Quieter, cooler (ever tried to A/C thatch?), fewer bugs, newer and nicer.