Have a look in Phase Eight & Hobbs for more expensive tailoring.

I do think that M&S have some good suits - particular mix and match jackets with skirts, trousers or matching dresses (I bought one the other day - dress was Ł15 jacket Ł35 !). I have to say they are my basic work staple with a good shirt & heels. For a more casual look, try a sweater or plain coloured cardigan over a shirt with skirt or trousers.

I like kitten heels as they are more comfy but still smart.