Getting started

Hello everyone,
I have just finished reading "Potatoes not prozac" and I feel like it was written about me. Something that Im sure everyone on this forum has felt too.
I have always known that I have an addictive personality, I do not drink much or smoke but addiction has always been food and coffee for me.
My friends and I joke that I can not have a box of cereal in the house as I can not just eat a small bowl, I eat the box in a day! I have even called it a cereal addiction, I know now that it was an addiction but not cereal itself but sugar.
I have been on many diets and I have always had an all or nothing approach in everything I do so ultimately I always end up failing.
A couple of years ago I followed what was basically a caveman diet, anything that we could have sourced naturally, no processed food and no cows milk, I lost weight but felt fantastic, I also dropped my caffiene intake completely so I already know how amazing I can feel on a high protein low processed food diet. After a holiday where I relaxed completely I slipped up and gradually I have put on all the weight I lost and some.
I have even more anger and disappointment in myself that I thought that I had found a fantastic way of life achieved something and I went back to all my old habits and feelings and depression.
Ok now to my questions and I really need advice because I already know how good I feel with a low sugar high protein diet I want to just start it now, I am scared to eat sugar now that I know what it is doing to me, I am also scared of failing if I don't follow the steps, I would be really grateful for advice please?
I was also wondering what calcium sources are best to eat? I would rather not eat cows milk but my mother has osteoporosis so it is important to keep my calcium levels up.
Also the big question coffee? Should it go?
Im looking forward to hearing from you.
jo