Well done, that's boody brilliant! So pleased for you :)
I know, changingrooms are cruel, cruel places, designed by men and/or size 6 models, I'm sure!!!
Personally, I've had very good experiences with WW in the past, I think they really make you aware of what you eat and help you consider your portion sizes, etc. I also really like their slogan "this time, loose weight for the last time" or something like that.
Personally, I'm finally at a stage where I am balancing my food intake with exercise and I've managed to maintain my weight pretty well now for about 6 months or so, but as I said, different things work well for different people and WW definitely taught me a lot about healthy eating habits so it was really helpful to me.
The only advice I would give is to stick with it, no matter what. My problem always was the slippery slope, I would have one biscuit and then think sod it, I've broken my diet now, might as well have 10 more, then continue feeding my face with everything I could get my hands on for the rest of that day, then get up the next day and think what's the point, I'm no good at this and start eating like a pig again... So now I would say, even if you falter or fall right off that horse and have a whole pack of biscuis, dust yourself off and get right back in the saddle, because in the end it's really, really worth it!
Be proud of yourself for having turned that horrible day yesterday into a positive one, where you've managed to take the first step towards a healthier, fitter, slimmer future. Good luck :)