Lucy
It seemed to take me ages and ages to move down my first size and I had the same problem as you. Existing trousers were way too big and next size down was too tight, but suddenly it will happen, so hang in there. I can remember how excited I was losing enough to go from a 22 into a 20, and today, there I was, trying on size 14 trousers (if anyone had told me I'd be doing that 6 months ago I would have laughed at them). I did buy the 14's today and if I was standing straight all day I might be able to wear them, but they are a little too snug atm. Should be fine in a week or 2 I think! If I were you I'd buy the next size down and try them on every week. You'll get closer all the time which is really exciting.