I lost 3 stone and have kept it off for 3 years.
Once I had gone cold turkey on my worst habits (uncontrolled unhealthy snacks, lots of toast, chocolate, biscuits) which took about 4 days, I relied on readjusting my diet.
In with a sustaining healthier breakfast (blueberries - frozen - plain Greek yogurt, a spoonful of high protein / low sugar granola). Lunch: one slice of wholemeal toast with a poached egg / sardines / avocado plus salad or veg soup or similar. I made salads from shredded red cabbage and carrots with a ginger and lemon juice dressing, cheap and filling.
One snack in the afternoon, planned, e.g an apple, or two oat biscuits and a thin layer of cream cheese, or a mug of cocoa made with cocoa powder (not hot choc) and half a spoon of sugar) , carrot batons and 30g of cheese.
Dinner: normal dinner but smaller portions of carbs, lots of veg. I started eating half a pizza with salad instead of a whole pizza with dough balls. Lean protein (I like chicken thighs with the skin off, fish, chick pea curries, etc)
Appetite adjusted fairly quickly. Lost about 1lb a week. Felt healthier and incredibly pleased with my success in seeing steady weightloss. Enjoyed the feeling that I was treating my body better. Chose foods I enjoyed. I did have loads of big lapses but just carried on with healthier eating the next meal / day.
Maintenance has been easy because the new lifestyle is easy. I eat more at lunch now (e.g another slice of toast, or a packet of crisps) and am relaxed about ‘celebration’ eating. (From cake with a friend to indulgent Christmas). I don’t think in terms of ‘treats’, all my food is enjoyable and the idea of a treat sets up a holy grail in my mind that must be pursued. I don’t eat snacks, except mid afternoon healthy snack.