Get yourself a good nutritionist. You aren't going to find your personal dietary needs on PC IMO. If you feel like venting or getting some casual advice, that's cool. But you sound like you need an overall balanced eating plan.
I have been through a lot of throwing up, starving myself etc. The only way I ever sorted out my eating was fortuitously meeting someone who is amazing about exercise and eating (e.g. knows a lot and knows what is healthy and what is reasonable). When I stick to his plans for me, I am happy with my body (and that is saying a lot compared to how I used to be).
I don't believe in buying all the 'healthy choice' meals etc. A lot of them are very high in sodium, and for god's sake, a 'creamy low-fat pasta'? Designed for DINNER? a) there is all sorts of additives to make it taste like that, and b) women in particular should not eat carbs after 5pm. Sigh. My theory is that they do that so people don't lose weight so fast and pay for their programmes and food for longer.
Size 12 UK is not 'fat'. I am 5 foot 7 inches and I'm probably your 10, although I'd be inching towards an 11 in my bewbs and butt cos I am just curvey there. An 8 is very small silver. Not very healthy IMO.
Maybe if you could lose three or four kilos you'd be fine? That's probably the diff between 10-12? And doing it a REALLY healthy way?
Also I am sure you know to not deny the treats every now and again. If I do I end up buying and eating a whole tub of icecream or brie and crackers or something hugely fattening.
Here I go giving advice, but I am not an expert and don't pretend to be.
You are not fat at a 12, honey. But I know it sucks to buy new clothes if you put on weight. You should not lose more than I think, 1kg a week, or it may actually be 1/2 a kg a week - I can't remember - if you wanna keep it off easily. I am sure you know this.
I just want to emphasise that a lot of the time it is not WHAT you eat, but WHEN you eat it. I learnt this the hard way.
Good luck ...