Ok, I appear to be shrinking, and will probably have to give in and buy clothes.
The last time I tried buying clothes online, I went to Boden. I looked at their measurements, I measured myself, and found I was apparently exactly an 18. Which was a bit weird, as by that point, all my size 18 clothes were hanging off me. So I bought a 16. Which fit fine.
Now, I am apparently exactly a 16 by Boden (I think, will check again). So does this mean I am a 14? Are there any websites which don't lie about the appropriate measurements?