I remember reading somewhere that the winters in Chengdu are bone-chilling, (might have been on this forum) but since I’m from the Nordic region, I’m used to -20C so what I’d call bone chilling is probably -30C. Hehe.
I’ve walked outside with only a T-shirt already just fine, but I’d still recommend having a normal coat. Doesn’t have to be a winter one in my opinion. (I don’t have one, I just use a typical thin coat if it’s very windy.)
But yeah, if your not used to the cold, prepare accordingly. I see most Chinese with pretty thick jackets still.