Now that I look more closely at your message, you just say "casita" on the beach rather than thatch cabana or casita. If you don't want thatch, there are some other places with cottages/units/casitas on the beach, including the Essene Way, Cayo Espanto (on the small island on the back side of Ambergris -- extremely expensive), Capricorn, Xanadu (interesting dome-shaped structures with thatch roof covers), plus various rental houses.
--Lan Sluder
Belize First