I lost 4 stone last year OP, and have been maintaining the loss for 6 months. I'm older than you, and like you thought that this time, I'm not putting it back on.
I lost it by eating around 1200 calories a day. I cut out sugar, ate only unrefined carbs in small amounts and lots of green veg, fruit and salad. I ate lean protein. I cut out sugar, ready meals, snacks, cakes, biscuits.
3 meals a day.
I maintain it by eating the same food, avoiding the rubbish, but eating a bit more - around 1600 cals a day. This might not seem a lot of calories but for my age, it's enough. And, because I avoid the sugar and eat healthy food, I feel that I eat enough.
I never snack between meals, or in the evening.
It's a way of life now, and I don't even think about it. Portion control, in my opinion is key - a lot of people eat the right type of foods, but far too much. Once I got used to eating smaller amounts, my appetite adjusted, I never over eat now.
Good luck! I'm sure you'll feel better - I certainly do.