Westfield is big, very big but is close to Holland Park and Notting Hill and there are some good hotels there
There is no point in going to the Tottenham Court Road side of Oxford Street, all of the department stores are around the Bond Street tube stop. Personally I love John Lewis, staff are so friendly there. Regent Street and Bond Street are in that area as well, very good for the posh side of shopping.
From a market perspective, Spitalfields near Liverpool street can be quite good, Notting Hill and Camden are quite touristy these days.