Suggestion on suit/dress Tailor in Bangkok. Will be there for 1 day then returning a few days later(to pick it up) We are staying at the Peninsula Hotel

That really isn't adequate time to get good tailoring done. You need to plan for at least three fittings. The women's tailor I recommend is Cotton House, in the Oriental shopping center behind the Oriental Hotel.

there is a tailor in the penn, but I doubt there is time

If you take something to be copied , you will do better with your limited time. JSThais silk on the second floor of Rivercity, just across from the Pen may be able to help with your time constraints. Ask for Penny. Tell her Karen and Bob sent you. for Men's shirts , just across the bridge that connects Rivercity to the Sheraton hotel is a shirt tailor who again , if you take a shirt to copy , could make shrts , but I doubt a good fitting suit. Royal Mantique Tailor. Good luck and have fun.

Yes, you can have something copied in that time, but then you have a replica of an off-the-track garment. If that is what you are looking for, fine. If you want something custom-made, that takes time.