French Connection black crepe trousers/skirts - pricey if new but they are fantastic. Don't crease, wash well and look much more expensive than they actually cost.
Buy them from ebay - size up if you are not too sure of your size and then get them take in to fit. Promise you they will last a heck of alot longer than cheaper alternatives. There are these on at the moment in a size 12 (no - not mine, I'm CTB on ebay too)
Or try ebay for LK Bennett, Jigsaw or Hobbs workwear stuff - try on in their shops to check sizing (and if their "cut" fits you). Again, you could get things taken in to get a better fit. Trousers taken in up the back seam shouldn't be more than £10-15