Congrats on getting back on a weight loss program. Get fit program. Try not to overdo it, pace yourself. No one needs an injury. At 52 I developed bursitis from my workouts after a decade of a sedentary lifestyle and it took many ice packs and therapy to get it under control.
As to your last question, do you mean TV dinners? Some friends advised me to "just eat half portions" of regular meals but how much we eat depends on what we know about nutrition, right? And calories and such. If we know a lot then maybe cutting down will work for you and you won't need boxed meals. Everyone is such an individual; we have our own ways of "staying on" our program, e.g., I don't like cooking and Lean Cuisines were great for a busy schedule and portion control. I still buy them especially now when I am working on getting off some regained weight. But I have also found out I can prepare some simple things like lean meats in a pita or chicken salads. There are all kinds of tips on the web for cooking up healthy foods. Print some out!
Keeping a food diary, btw, is a smart idea. I still keep track of weight, calories and measurements in a little book. It's my reality check book. Good luck!