Certainly, from half a world away, I could have easily missed the mark on this one, but I hope you didn't miss the point. I do not know the exact genera of the bird you had, but I still bet it was some kind of flycatcher. There are nearly 40 different ones recorded as being resident in Thailand. The previous picture was just a handy example of one species, of which there are over a half dozen subspecies. Within the species, they are very different in size when adult.
To illustrate my point, here's another flycatcher resident in Thailand.
https://teakdoor.com/images/imported/2006/07/228.jpg
I'll stick to my flycatcher theory, but will courteously back down if proven wrong.:)