If you're going to do it yourself, I have one very , very strong suggestion.

Tweed. Tweed, tweed, tweed. Tweed is very forgiving of little imperfections. Fine cut cloth like what goes into tuxedo jackeets, is not.

Hie thee down to the jumble sale, or the discount clothes place, or even the Goodwill store and find a tweed jacket that you like, and modify THAT.

If you're going to pay a professional tailor to do it, that's different.