Gap sale rails - just found my 7yo a lovely sweater dress, just plain cream wool with a fancy-stitch upper bit. They had them in sizes up to 13. (Very nice with leggings, if you're not wholly against leggings.)
I like Zara too, though haven't scrutinised their bigger girls range - they do have some nice plain stuff for boys - so girls' stuff likely to be OK (by analogy of comparing Zara big boys' stuff to H&M's (the latter very skully-hoodie)).