How exciting!!! I love it that you're bringing the wedding forward
I am also v jealous that you're a small 12 and you're the same weight as me and only an inch taller *sobs*
Anyway, back to dresses, this is about you not me!! As Fern said, you should definitely get out there and try loads and loads on. Don't have any pre-concieved ideas of what your dress will be like. Open mind and just try...you'll be so amazed at what suits you.
You've not got heaps to lose so it's not like your body shape will change dramatically - what suits you now will still look gorgeous at your target weight.
Don't be surprised if the label in the dress you buy is a 12, 14, or even 16! Wedding dresses are sized very differently to normal frocks in shops. They've got much smaller size intervals as they're more made to measure (usually) and so there's less adjustment needed (usually). You'll be measured when you order and most manufacturers have different size charts. Just to prepare you!
Oh, and also, the shops will all have wildly different sample size dresses. Some shops I went in had all size 10s, some had a range from 6 to 26...it will vary. It's sometimes hard to visualise how a dress is going to look on you if it's way too big or too small. They will obviously pin you into it as best they can, but sometimes you need a bit of imagination and vision to work out how it will look on you.
Don't worry about autumn wedding - I had mine in September and it was glorious. I had a spring divorce instead! LOL! Off-peak weddings are also cheaper at venues.
How super, super exciting! There are SO many nice dress shops around. If you want any help, let me know, as I know lots of the good shops. Ok, so it might be a bit far for you to come down towards Preston, lol, but there are some a-ma-zing dresses in some of the boutique shops round here.