Fruit is really awesome to give you substance
. Bananas are well known to be filling, but apples, oranges, melon, you name it, are low calorie, sweet, and filling. If you find yourself craving carbs like I do (maybe that's what you mean about the full feeling?) eating whole wheat bread is good because it gives you the fiber and grains you need (yes relatively high calorie, but also needed for energy). I personally like crisp bread like ikea's knaakerbrot.
The key is to figure out how to balance your meals. I would say, using traditional food, you want to go with the 1-1-4 ratio: 1 serving (size of your fist) lean meat/protein, 1 serving carb (again, size of your fist--potato, pasta, bread roll, etc.) and 4 servings of veggies/fruit (mixed greens, mixed fruit, steamed veggies, stir-fry veg (use that pam spray
)). You say you eat unhealthily, how so? Too much fast food? Too much calorie laden sauce, too much sweet stuff, etc.? You need to analyze your food habits (I, for example, eat too much bread and savouries, so I try to fill up on fiber-high foods, like green veg and fruit) and translate your now habits into healthy habits. Like sweets? Maybe figure out how to incorporate fruit into your meals (think of using pineapple in curries, etc.). If you like fried foods, maybe try just covering a chicken breast in breadcrumbs and baking it. It's all about figuring out how to change your habits, not starving yourself or abiding to strict rules. You can reward yourself every once in a while (sort of like a good saver...every once in a while we all splurge, its just not splurging all the time, if that makes sense
).
Additionally, not low calorie but certainly good to consider: Trail mix. Lots of energy, good oils, and so tasty. As a snack it is much better than reaching for the twix