Sleep - I can only tell you what my fantastically competent dietician said and that is (1) "good" carbohydrates = slow burn fuel for the body, and they keep you feeling full for longer, and (2) you should have a bit of carbohydrates with every meal to make it to the next without either hunger pangs or raiding the cookie cupboard.
I know that we instinctively cut out carbs when dieting, but that is not in your long term interest, because if you don't (1) you will be hungry, which is counterproductive when dieting, and (2) when you start eating carbs you will put back the weight you lost.
Imagine your plate. It should always be half vegetables/salad with very little olive oil, quarter protein (1 egg/1 chicken breast/equivalent in fish etc), and quarter carbohydrates (5 spoons of rice/pasta or a slice of bread).
I have exact measurements somewhere, if anyone is interested, but I have kept to these visually approximate measurements and I haven't put any weight back on since then.
Re yoghurt & biscuits - Check out the calories and the fat content on the box. You will see that Greek yoghurt is always higher in calories than normal yoghurt (I can't talk brands because I live in France and don't know UK brands). Also, find some plain biscuits that is about 35 cal per medium size biscuit, most of which are from flour (rather than sugar and fat). Carry two with you as a mid-afternoon snack, with tea or coffee. You will be amazed at how easier that diet gets.