Maybe diet (tracking what you eat every day in the food log and sticking to a calorie limit) will be more effective than just ramping up your exercise, at least in the beginning of a diet. I say that because of your past experience with injuries stopping your progress. Unless I misunderstood and you just happened to have the bad luck of experiencing injuries (not exercise-related).
You say you have a sitting job. Is it at a computer? Can you elevate your monitor and keyboard so you work standing up? Just build a platform (I have my keyboard on a suitcase) to keep those at eye level while you're standing.