If you have time - check out websites like
www.chadwicks.com -- it's fairly conservative but reasonably priced clothes..
For the short term....
Dark Skirt (knee length)
Dark trousers (dont wear on your first day until you see if other women wear trousers)
White button front blouse
Jacket that matches the skirt (generally solid color jacket and a skirt in a plaid that matches)
A sweater set or two
Hosiery is probably essential