white regency dress Swiss Dot the Bridgerton Costume Analytics: A White Wedding
Description
I had to piece the fabric because there wasnt much left, and the leftover fabric wasnt very wide but thats period accurate (source)

Show Me Your Mumu Emily empire maxi dress in Steel Blue Chiffon, $188, Show Me Your Mumu 17

Made from stretch satin
Also if the dress has a beautiful back, a bow helps to emphasize it and make it look stunning

Thin, flexible wisps of spun glass could be woven with silk fibers to produce fabric
