I know that cotton is best for children with skin problems so stick to it for DD where I can. DD has eczema and psoriasis but the worst is on her cheeks and last year she had a wool duffle coat that made her skin so bad she couldn't wear it. But the puffa coat I got her wasn't much better, she maybe was too hot in that?
So what do others do? I'm looking at Gap's warmest coat and was thinking that as i is better quality than the £15 coat from last year, it may be more breathable material. But then if its not its an expensive experiment! I can't seem to find a warm coat in cotton though.