Originally Posted by SeamasterLux

Might have missed a few mistakes, my bad!

Flannel you find pretty much everywhere. Depends what you're looking. If you want the fabric to commission something with a tailor, you can order with Holland & Sherry, Lesser, Minnis, Harrisons of Edinburgh, etc. (a lot of drapers)

If you want to buy off the rack not too expensive: I'd recommend Suit Supply and Boggi.

Higher-end options include: Borrelli, Caruso, Ring Jacket, La Vera Sartoria Napoletana, Ralph Lauren Black or Purple Label

Even higher: Isaia, Loro Piana, Brunello Cucinelli, Kiton, Sartoria Partenopea, etc.