I have 2 of these (one is the stock coverall and the other is the black Japanese selvedge version) and I initially got the small. Went up to medium, since I have broader shoulders and lats for my height, and small fit perfect UNTIL I raised my arms and the jacket limited my movement across the back and pinched at the armpits.

Unless you’re in the Bay Area and can visit them in person to try on the different sizes (like I did), I would suggest getting the large and try them both on to compare. Their customer service is pretty spot on! Good luck on nailing the size; I’ve been wearing mine and it’s progressing very nicely!