How to stick to it?

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I'm fat. Not huge, but definitely fat. I've yoyo dieted all my life - biggest after twins in 2007 (size 20), smallest after low carbing in 2012 (size 12). Now, as very often over the years, squeezing into a 16. I'm also short, so I can't get away with being a 16, and I'm v pear shaped, so my bum and thighs are big always which I completely detest. I want a straight up and down teen boy body, but realistically I'm going to have to settle for a 40 something, flabby, curvy, woman's body. But I REALLY REALLY want to be able to buy clothes without crying. Which means being a lot smaller. I don't want to do another diet because I've done them all, they all "work" and I fail because sooner or later I get lazy or sad or hungry or upset and the weight comes back. I need to change my eating habits for good. I also cook for 8 people every night including veggie and gluten free options, so I definitely can't add in any special diet menu. I mainly need to eat less and make better choices like not eating a large Easter egg in one go.

Sorry, that was long. So the question is, what do you think works to find the motivation to stick to a plan? What can I do to succeed on this and stop hating myself so much? Is it worth trying hypnosis, or anything else that might help? Or does it just have to come from inside?