You lucky thing 
I agree with Cos and Zara, also Massimo Dutti, lovely things that look v expensive in RL. They sell online now. Also Topshop, fashion insiders adore TS, Emmanuelle Alt (editor of French Vogue) will only buy her jeans there apparently.
Stick with black, navy and charcoal. Fashion industry people love the combination of black and navy, but it must look like you did it on purpose! Accent colours for tops and accessories.
These shoes are highly recommened in the W&A thread, look expensive and are v comfortable. These boots are the business
I have them and wear them with skinny trousers or short skirt and opaques. They are a copy of Celine who did boots with gold heels last winter.
Could you borrow a bag or 2 from a friend. Ideally you'd need a work bag, Mulberry Bayswater size and a clutch for your evening do's.
So, cigarette trousers, pencil skirt, 2 silk t-shirt tops,2 pretty silk blouses, 1-2 dresses, 1 blazer. Also don't forget a coat, maybe a trench.
Accessories - a couple of 'statement' necklaces (try Accessorize or Topshop), a couple of scarves (Zara & Dutti good for these)
Will be back with more, but only if you promise to spill the beans when you come back!