Many teachers who have been around longer (American and various Asian nationalities) do not live in Thana City. Some live far away because that's where they lived before coming to TCIS, some live in Bangkok, some live in other housing complexes out here near school. If you want to live downtown, or at least closer to it, you definitely have options, so long as you're willing to rough it in a hotel while you're looking for a place.
It's hard to beat living near the Skytrain for one. It is a traffic-free route to many very cool places in the city. The part of the Skytrain that is nearest school (SE side) is the On Nut end of the Sukhumvit line, which would be stops Phrom Phong, Thong Lo, Ekkamai, Phra Kanong, and On Nut. These are Sukhumvit Sois 26 up to 71 or so, in the districts of Bangkok known as Khlong Toey and Wattana.
Other areas not on the Skytrain route but closer to town and
TCIS would include Bang-Na and Srinakarin Roads. By the way, there is a
proposed extension to the Skytrain that would run out to the New International
Airport…which is in Thana City's backyard. Unfortunately It would
be many years in the making…