Ooops, sorry Enpi, just rereadyour post and see that I misunderstood your travel dates.

Late December would be peak season and you won't get Woodlands for the price range I mentioned (more like 3000-3500 at that time. Cosy Beach will be busy and therefore no good if you can't get around the pool - when WILL hotels stop guests from 'reserving ' sunbeds with towels and then disappearing for hours ????????????
Pattaya is very popular with European tour groups so lots of places will be busy/full.

You could check out some internet booking sites and get an idea of prices and locations and then ask on here if anyone can comment on particular hotels.