A friend recommended http://www.pinkytailor.com/ for when I pass through Bangkok – rubbish website, good tailor.
Will you be staying in one place for long enough to go through the process? Usually it’s initial measurements in one visit, then a fitting and likely a second fitting (even more if you have time) to get it spot on. Obviously there will be some time between these.
Have a look around at suits before you leave and get a feel for what you want – if you can take along pics of what you want, all the better. Think about things like lapel shapes, rear vents, jacket/trouser pocket types, pleating, etc.
http://www.asuitthatfits.com has a wizard with lots of options that will give you some ideas.