I hate to say this as it might come across quite evangelical and I don't mean it to. But if you can reduce ultra processed foods as much as possible it might surprise you.
Dr Chris van Tulleken did an 'experiment' where his diet was 80% UPFs (like a lot of the population). What particularly interested me was his brain scans afterwards. New neurological pathways had been created in the reward centres in his brain, which basically means the more UPFs he ate, the more he wanted, and the more reward pathways were created, which created this vicious cycle similar to addiction.
So don't be down on yourself about 'willpower', it's not that you're weak or not disciplined enough. But most prepackaged foods are UPFs, and they're changing the wiring in your brain to make you want more.
Our options at supermarkets are mostly UPFs, so it is insanely difficult to stop completely. But speaking on a personal level, once I realised that having one biscuit would make me want the second and the third, it was easier to not have the first iyswim. If I want a snack I try and find something that has less than five ingredients, and it's been a gradual changeover and awareness of the effect on the brain for me that has inadvertently helped with the 'willpower' side of things too. It's not about 'making healthy choices' (I eat way too much cheese
) but avoiding that rewiring in the brain that goes on when you eat processed food, and just keep eating.