I agree with the suggestion to book the Sheraton Grande Sukhimvit. At those hours, it doesn't take long at all to get to and from the airport (less than 30 min) and a taxi isn't very expensive (less than $10 each way). You'll probably get a nice upgrade and have a nice room at the Sheraton. You'll enjoy extremely spacious comfortable bath and showers. If you've slept on your flights and want to explore a little, you can still make one of the night markets or have a late dinner in town.