You can always have the bigger one taken in a little bit at specific spots like the waist or sleeve width to make it fit like the original.As the original poster of the thread this was the exact same problem I had when purchasing! Between these two sizes. My arms used to hurt in the 36 at first, I could do it up but could not really love my arms but it did loosen up. That size then became faulty so I was able after 6 months to return it and opted for the bigger 38. Whilst the 38 is more comfortable it doesn’t quite clinch in at the waist the same, though I wouldn’t buy a jacket for this price that I can’t do up so if you’re unable to close it yet the bigger size IMO.
Post pics and we can give you opinions
Just make sure you use a very good seamstress. If you’ve never tried her before, don’t give her your Balmain jacket first, unless you took the jacket to Balmain. Fix another jacket as a ‘tester’ first and if that’s fixed to your liking, then go ahead with the other.