Adams Kids I have found good for my Ds have the adjustable waists on a lot of stuff. They do online. They have recently closed their bigger stores but do still have smaller stores worth checking if there is one near you.
Tescos trousers tend to have the adjustable waistband in, and they're nicely priced too! Also, quite a bit of their girls stuff can be plain or more loud and funky rather than girly and frilly. Also, next's t-shirt multipacks tend to have 'tapered' or fitted waists, as do a lot of mini mode's stuff in boots. Don't knoww why though!