baghag, i have two balmain jackets with the shoulders, im like you, a 34 or 36 in balenciaga, and in balmain, my black one is a 34 and my white is a 36, they all fit well. the 34 is tight around the arms but its a cool look...
the thing about those jackets isnt a problem of getting a smaller size, but if you size up , you will end up looking like a football player! the first balmain jacket i tried was in a 38 and a SA tried to convince me on how cool it looks, my husband looked shocked! lol, i didnt like it either, so left the store, went to another , tried on the 34 and wow...my husband loved it and so did it..the shoulders dont look so crazy when the fit snuggly...ill take pics and post them so you get an idea