DD is 10 and I usually buy her winter coat from M&S each year. Plain, warm, long (she really feels the cold quite badly) but the main thing I had trouble finding this year is velcro rather than buttons to go over the zip up part. She has some specific special needs which mean she really struggles with zips and buttons. She can just about manage them but often in a rush will want to cheat and just put the velcro bit together. In the depths of winter she will do up a zip provided it is a good quality one that can cope with a lot of pulling on it as she struggles with it. She is at the age where she doesnt want to ask someone to help anymore.
I have searched online Next, GAP (they did a nice one she wore a few years ago), M&S and even Boden and Littlewoods. My experience of Sainsbury's one year was a broken zip in less than a month. I dont think they have the quality though I buy their cheaper stuff where I think I can get away with it. Where else can I look?