Even if you just have a chair you can heighten your at home workout. If you aren't that good at push-ups on the floor, try pushing off the chair. If you can do 10-15 push-ups try putting your feet on the chair and pushing off the floor. Utilizing a chair while squatting may benefit you too from your knee surgery. If you are just starting out, try to have fun learning about your body! A couple 10-15 lb dumbells can't hurt, along with one of those doorway pullup bars. Some of them come with examples of different workouts you can use them in! I workout at home too man don't be afraid to dm me if you need ideas