Totally depends on your office and style.
I wear all the following
Shell top, unstructured jacket, cigarette trousers and flats (brogues/slingbacks)
Polar neck jumper, slim trousers, brogues.
T-shirt, long cardigan, straight leg trousers, flats.
All in neutrals, so light grey, beige, fawn, white, black, navy, cream, toffee.
I shop from COS, Other Stories, Theory, M&S, Massimo Dutti, etc..
Our dress policy is smart casual or business wear if client facing.