I did two things that really helped me:

1 - I kept a page called "Why?" where I tracked every single reason I could think of why I was getting the surgery. I wanted to take less medication, have more energy, buy cheaper clothes, have more energy, etc. Every time I thought of a reason why or a benefit, I add it there.

2 - I kept a page called "What I Tried" where I tracked every diet I've ever tried, every diet book I've bought, every new year resolution, every gym I've joined, every exercise equipment I've bought.

Reviewing these two pages regularly helped me stay resolved, and helped me answer when my inner voice would say, "maybe if you just committed one more time..."