My nine year old has the narrowest feet. I'm struggling to find a pair of wellies that don't slide up and down and rub his heels badly. We live in the country and wellies are an essential! Any suggestions as to brands that are good for super narrow feet? He's a 2.5 so just about in small ladies sizes so would happily look that way if necessary. Have already tried agile after being told they were narrow but they're still like wearing two boxes on his feet!