Apart form the unintentionally short coat and short sleeves, I cut the size S-M but added 1" to the fold of the back piece (so 2" in total) and thus added they same to the collar piece that joints on to the back. I felt the S-M would be too small and it would've been - the extra 2" across the back makes it wearable.
Pattern: Brooklyn Coat by Tessuti
Modifications: as per the above blog post
Fabric: boiled wool from LOOM
Changes for next time: sigh...I don't even know where to start!