The key to personal style is understanding your individual beauty enough to know which looks will work for you and which probably won't.
Don't get hung up on the size. If you feel bad about yourself because a 12 is what fits, take a Sharpie, and write '6' on the label.
I know what it feels like to struggle with your weight, and it makes me understand why women get attached to numbers on a scale or a dress size. It doesn't mean that I have gotten over all of it myself, because I have good days and bad days just like everyone else.
What is magical and mystifying to me about style is not that by seeing we can believe. It is that eventually, we can believe, because we can see... we can embrace change the more we can make it tangible.