I'm in my late 20s *sob* and I am getting pretty much all my clothes at Oasis at the moment, they have good flash sales if you're on their email list and there's normally at least 20% off floating around. Their dresses and tops are very feminine (which is my style, sort of a geek twist on retro/vintage) and they use good fabrics for the most part. I am wearing a dip hem hummingbird dress over an urban outfitters shirt to work today from oasis
I would say that if you're tall, things come up both short and a little small, so for instance I'm 5"8 and anything mini is micro, anything knee length is a couple of inches above. That may be because I'm short waisted and long legged though
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Also they do 90 minute delivery, which I am ashamed to say I've taken advantage of more than once
www.oasis-stores.comI do like Zara and Mango as well, although if you're busty you're struggle with Zara, and Mango's sizes are a total crapshoot as they do SML :/ but they have the most amazing knee length, long sleeved, heavy jersey dresses
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Dorothy perkins is also totally reliable, you can exchange in store which I really love.
I can't stand HM for anything but the most basic stuff, or fast fashion things that I'm going to wear a couple of times (a sequin blazer type thing).
I feel like I'm too young for banana republic for the most part, or at least I don't get their aesthetic, but I do have a couple of things from there, they seem to do totally unannounced "happy hours" where everything is 40% off really regularly, like pretty much every time I end up at Westfield during the week, which makes them much more affordable.