It is very helpful infomation for me.
I think it's great that you're careful with your body image, but don't obsess too much over it. Try not to weight yourself too often either, or use the quantum scale, the one that records your weight but doesn't display it, it just tells you your progress. The reason I'm saying this is because when your weight reaches a plateau it gets harder and harder to lose those pounds and you might begin to feel frustrated and lose motivation.
Stay positive, keep a good attitude and I'm sure you'll be just fine :D
I'm not as familiar with everything involved the Slimming World diet plan. But I can't help but think that as you grow muscle mass and maintain a high level fitness, you might be finding that 126 is an appropriate weight for you given your bone structure and height. I'm curious how much weight you are hoping to lose...?