Personally, I'd give the opposite advice to "look in 'everything 5.com". It's cheap tat that won't fit well and will make you look worse.
Shops seem to have divided themselves lately, either courting the wealthy teenage market (by which I mean age 14s) or the wealthy middle-class mum market. This means you have Boohoo, Missguided and Forever 21 in one corner (it doesn't wash well and often looks cheap) and White Stuff, Boden, Joules and Seasalt in the other corner (items are often of better quality, although that hasn't been the case for a couple of years - more polyester creeping in, more bobbling on washing, I think.)
Neither are really a great option. Too cheap and it looks, well, cheap. And the Boden-esque prints look frumpy, mumsy and old-before-your-time. They seem to keep cutting their sizes bigger every year "to hide your lumps and bumps lolz hun" and everything becomes sack-like.
So aim for somewhere in the middle that still wants young women customers. Zara, Mango and Oasis and their ilk. If you want to spend a little more, Cos and &Other Stories are popular (but too grey and boxy for me.) Browse instagram and, if you see styles you like, find out where they're shopping.
I like Hollister (the unbranded stuff) as well. Fits well, washes well. I also like US brands like United By Blue and Ten Tree, which is fantastic quality and ethically made.