Whether its to sustain your natural posture or improve it - developing your core muscle groups is the key. If you are experiencing the MS "hunch" either due to wheelchair reliance of gait issues you can overcome the results by strengthening and building your core muscle groups. Sit-ups and crunches improve the look and tone of those muscles but to realize better posture those are a must along with effective twist exercises as well to develop your obliques. The Russian Twist can be done while laying on your back (even on your bed if necessary). bring your knees to your chest in a 90 degree angle and with hands clasped behind your head, bring opposite elbow to opposing knee. for more advanced exercises you might try a weighted Russian Twist while holding an appropriate dumbbell. Other at home exercises are a Criss-Cross, Windmill, Standing Bar (or counter) Twist ,or even lunge twists which are all pretty self-explanatory.