One thing that I find to be true is that the one little cheat is more than that. The cake or cookie or ice cream will influence cravings later. That doesn’t mean you shouldn’t cheat. I believe the best way to succeed on a diet is to set up a cheat system (stick to the diet the whole week and get a small piece of cake for Shabbos or allow yourself four bites of cheat food over a day, etc). After the “cheat”, have something healthy to go back to diet mode.
If you aren’t used to exercise, maybe start by going for walks. Its not to strenuous, calming, and healthy.
The hardest part is making a decision to change and starting. Set small goals and reward yourself when you keep them (not necessarily with food) and don’t lose sight of the goal.
You can do it!
Lots of Hatzlacha