Couturier

Couturier is a French that than means “dress maker”. In English it means a high class dress design house or dress maker.

Chanel, Dior, and Givenchy are some of the great French couturier houses.

Merriam-Webster Online Dictionary
couturier (noun)
an establishment engaged in - couture , also the proprietor of or designer for such an establishment
Synonyms:
Dress maker