I would venture further off than Khoa San rd., to see more of the city and get away from 'farang-land' if nothing else. No specific recommendations, but if you happen upon a tuk tuk driver you like, try to swing them into the deal as well: they get 'gas vouchers' from various tailors and gem salemen for bringing farang to their shops. If you actually buy something, they get more - so if you know you're buying, try and convey this to them, they may get set up and give you their # to become sort of a regular driver while in town, for cut rate prices. I had this arrangement with a guy, 'Sey ten', even though I didn't buy big, I had time, let him take me to several places where I feigned interest just for the vouchers, then he would set me up whenever he could - plus it added to my hilarious and appropriately BKK deboucherous slogan: 'Satan is my tuk tuk driver'. I'm still thinking about having bumper stickers made...

Hello folks
I have a friend that lives in Bangkok and he uses Savile Row Tailors on Suriwong road. He and his colleagues use this tailors for all their business suits etc
I am traveling to Bangkok in December and will be using this tailor when I arrive; I have used them so I can guarantee their quality of work. As for price
I could say reasonable
Hope this helps
Joseph

Probably too late for this too, but while I was there, I was at Crown Tailors in Sukhumvit Road soi 8. An excellent tailor in my opinion. Very helpful and patient throughout the process.