hey guys, i've been working in bangkok for a few years. if you're looking for someone to hit with let me know!
as far as i know, there are NO indoor courts in the city! all of the ones listed below are hardcourts (aside from them, there are a handful of other courts i know of but have never played at):
Soi 26 -- book in advance, 250 baht per hour. also there are some great knockers and coaches here. courts just moved about 100 meters from old location, so brand new.
Tobacco Monopoly -- book in advance, 90 baht per hour but i think you need a Thai national to book it, i play there with my (Thai) coach. courts a little worse for the wear but totally chilled out place to play and super inexpensive
Conrad Hotel -- book in advance, 500 baht per day. two courts, in shade.
Nai Lert Park Hotel -- book in advance, i think it's 500 baht per day for visitors, we joined for the courts and proximity, it's actually very reasonably priced and a very nice pool, too! two courts, well maintained.