Puzzled conscientious shopper in the UK. (ethical, fair-trade)?

i want to be conscientious in my purchases, especially when it comes to clothing. but i also want to be able to walk into high street shops and try the clothes on before i buy. i've done some research and i know that some companies are better than others but what i'm looking for it a simple list. is it more 'evil' to buy the top i like from one shop or the other. all i find it too much information so my mind is boggled and I refer to the default's of quality and fabric. does such a list exist and if so do you know where i could find it?