If you want to go shopping I suggest you go to John Lewis, or Peter Jones. They have lots of outlets such as Toast, Jigsaw, Hobbs etc and you can often find what you are looking for there. I bought a t shirt dress from Cath Kidston a couple of years ago and very comfortable it is. I am not sure if they still do them. Uniqlo are great and their flagship store is opposite John Lewis in Oxford Street. You could also try Cos on Regent Street, they have lots of simple styles in great colours, have a look at their website, but they always have new stuff in the shop that's not on it.