If you were going to Ambergris Caye and staying at Banyan Bay, probably the best option for you is one of the nicer places in Placencia.
My top suggestion would be Inn at Robert's Grove, which we rate the top mainland seaside resort. This small upscale resort has a lovely seaside location, attractive rooms with A/C, excellent restaurant, roof-top jacuzzis, tennis courts, swimming pool by the sea, good dive boats, and charming hosts. Try to get one of the junior suites -- worth the extra money.
Other choices there would include Rum Point Inn and Kitty's, and also Luba Hati. However, if you're a Banyan Bay condotel type of person probably Kitty's and Rum Point wouldn't appeal as much to you, and I don't think Luba Hati will re-opened for the season at that time.
Belize First Magazine and Fodor's http://www.turq.com/belizefirst/