I chose the 3/6 coat and unfortunately it was too small. My baby has just turned 3 months and it doesn't fit. The torso area is pretty short compared to other coats I've purchased, it's the length of a couple of 0/3m coats that I own. The coat wouldn't even close over his shoulders, he wasn't wearing any additional layers either, just a standard onesie.
Luckily I also purchased a 6/9m coat since winters last long here. That one fits him perfectly, for now.