Brummel’s morning dress was similar to that of every other gentleman. Hessians and pantaloons, or top boots and buckskins, with a blue coat and a light or buff coloured waistcoat, of course, fitting to admiration on the best figure in England. His dress of an evening was a blue coat and white waistcoat, black pantaloons, which buttoned tight to the ankle, striped stockings and opera hat; in fact, he was always carefully dressed, but never the slave of fashion.
Brummel’s tailors were Schweitzer and Davidson in Cork Street, Weston, and a German of the name of Meyer who lived in Conduit Street. The trousers, which opened at the bottom of the leg, and were closed by buttons and loops, were invented either by Meyer or Brummel. The Beau, at any rate, was the first who wore them, and they immediately became quite the fashion ,and continued so for some years. – English Eccentrics: Beau Brummell, John Timbs, p 22-35,
Mr. Brummel in his morning dress
A good humoured baronet, and brother Etonian of [Brummel’s], who followed him at a humble distance in his dress, told me that he went to Schweitzer’s one morning to get properly rigged out, and that while his talented purveyor of habiliments was measuring him, he asked him what cloth he recommended? “Why, Sir,” said the artiste, “the Prince wears superfine, and Mr. Brummell the Bath coating; but it is immaterial which you choose, Sir John, you must be right; suppose, Sir, we say Bath coating, — I think Mr. Brummell has a trifle the preference.” – The Life of George Brummel, Esq, William Jesse
More on the topic: Between a Gentleman and His Tailor, Georgian Index
Jane Austen's World 
Haven’t read this biography of Brummel, but as he is eternally fascinating I will find a copy. I must assume that, as it is being quoted here, it is an excellent book.
Oh! This is Captain Jess – so frequently quoted in the modern biographies. I snagged the pdf from Google Books. A hardl copy seems a vary rare find indeed.
I think you might find a rare hard copy in an antique book store. That is why I praise Google books for making this classic accessible to us.
If you search Addall you’ll find a lot of reprints and POD facsimiles, and if you want to spend a few hundred dollars, some old ones too.