I was going to suggest H&M as they all seem to have the adjustable waistlines, but I see you don't get on with them. I hate the in between sizes stage, Belle's at that at the moment. Her smaller leggings are just a bit too short and the next age are HUGE! Same with trousers, she still in a pair from H&M that are size 9-12 months! I bought some more recently in age 1-2, and they have to be turned up about 3 times! At least they will now last her!