We had a great time in Hua Hin (and Thailand overall). Based on advice offered here, my wife had one garment made in Saga in Hua Hin. It was just a copy job and was well tailored and good value.
She also had a dress made in Nickermann's in Bangkok and we were very impressed with them. The big problem with (especially women's) tailoring in Thailand is being able to trust the quality and authenticity of the fabric being offered. There are so many plausible silk imitations that price seems to be the only trustworthy reference. For that reason, paying a bit more in a reputable establishment is probably a wise investment.