We have been going to Bangkok for the last 25 years and tried out several tailors in different areas of the city. Rich Tailor is a small shop run by a Thai couple and offers excellent service at very competitive rates. You can have them copy any type of clothing (usually ready within 24 hours) and they will make an exact copy of everything piece. Prices range from 1000 THB for a blouse/shirt to 1500 for a skirt and simple jacket. They also accept that you bring your own material (e.g. linen) as the choice in some tissues might be rather limited. 100% recommended if you want to be sure to have a job well done!