You actually sound like your breakfast isn't big enough to me, but then I am a super big eater. I personally think that full-fat is the healthiest option when it comes to dairy and prefer unhomogenised full fat and the greek yoghurt must be the 10%fat one. If your muesli has a lot of fruit that isn't great for you, but I wouldn't worry too much.

My advice would be to eat as much good healthy food as you feel like and exercise moderately and don't worry about your weight. Health is more important than how you look