If you're still ambulatory then you should maintain this ability, and walking on a treadmill is a way to track your progress. A decent treadmill will not only record speed and distance, but will enable you to change the elevation at which you walk, which can strengthen your legs and increase the stretch reflex in your calves. Your training is not just about strengthening the muscles, it is about getting your nervous system to respond, so use variety in your walking patterns.
lying back on an exercise ball will give you a good stretch for your lower back and hip flexors. Using a ball in place of a chair will force the muscles that maintain your posture to work harder, which will help strengthen them. A ball can also be used against a wall as a support to perform squats. With the ball in-between your back and the wall, squat down as low as you can and stand back up. The ball will help you maintain proper posture and keep you from falling.
An ergometer it's a bike like that sits on your table and you
use your hands to rotate the peddles.
You can also buy exercise bands in light to moderate resistance to work your arms and shoulders.