[Help] Pattern Splicing? Sewing Machines Parts and Sales in Los Angeles

Okay, so, I’m cosplaying Tet from No Game No Life and I’m having some major issues trying to figure out how to make the jacket. I am making the whole costume from scratch (jacket, shirt, pants, wavy-tail-thingies,) except for the hat. For the hat, I’m just taking a brown newspaper boy cap and sewing on some stripes.

My original idea for the jacket was to just take my shirt pattern in a size larger and just make some adjustments (like cutting the front down the middle and hemming it, adding a hood, ect.,) but the jacket is way too large and doesn’t seem to be working the way I want it to. I’m kind of putting the jacket on the back burner until I figure out what I want to do.

Does anyone, please for the love of my sanity, have ANY suggestions or any pattern splicing tips or ideas for the jacket??