Living in BKK for 10 years I can tell you that BKK at this time of year is one of the best times to be here. Weather is good, prices for hotels are good, because most people have left fthe capital for the holidays.
Bangkok Marriott resort on the river is an excellent choice with an amazingly good Sunday brunch, Peninsula also fantastic.
Phuket, Samui are all tops for ripping people off on rates at this time of year.
V Villas at Hua Hin offer private Pool Villas and although rates are high, it is a great place and only 2 hours from BKK so save on extra flight costs and hastle.