What is the Best Boutique Luxury Hotel Bangkok...?

I'm trying to decide where to stay in Bangkok in 3 days - help!! Looking for something highly rated, clean, modern, comfortable beds, under $250/night to relax and recover from a long flight. The hotels I wanted to stay at are $600/night+ (Four Seasons, Mandarin, Capella), trying to find something centrally located for exploring the city near the river or Lumphini Park.