I think you should ditch all that yoghurt eating!
How about replacing the oatcakes with a couple of boiled eggs for breakfast? Make them how you like them, add lots of ground pepper and eat slowly, enjoying it all.
About a year ago (maybe more now) I switched DP and DS's packed lunches to proper healthy ones (I have been taking healthy lunches into work for years, but for some reason just gave DP and DS a more boring lunch and less healthy)
Now we all have either a big tub of mixed salad(lots of veg basically, not just leaves) with some sort of protein in it too (fish, eggs, prawns, chicken, chickpeas, chunks of nice cheese) or a tub of chicken pasta salad (not much pasta though, mostly veg again like peas, green beans, tomatoes, cucumber, chopped up apple, raisins, peppers and a sprinkling of curry powder and squeeze of lemon juice) or leftover roasted vegetables and roast chicken, or brown rice and vegetable stew (agian leftover form the night before) or a spanish omelette and salad, or wraps stuffed to bursting with loads of veg and a bit of chicken or tuna or cheese.
Basically for lunch I pack mostly vegetables, plus some protein, plus sometimes some carbs (brown rice, pasta, wraps or potato and other veg). We have fruit as well, for our 'sweet' thing.
That keeps us going till supper time.