Lean meat, chicken, fish, beans, nuts, etc will provide
protein. Low/no
fat dairy, including milk, cheese, yogurt will also provide protein, along with calcium and other vitamins and minerals -- aim for 3 servings/day of dairy. Veggies will provide plenty of fiber to fill you up, plus vitamins/minerals that your body needs.
Your knee problem could be because you are carrying excess weight -- that's a problem that I have also.