You should strengthen your trunk, neck, shoulder and arm muscles and it seems your hip muscles can also be strengthened a little, but, I would advise you against working the muscles too hard or else the contraction of the muscles will decrease its strength and if continued, will finally cease altogether. General fatigue will set in and if exercises are continued, signs of bad posture or gait will become habitual. You can try the following exercises:
1. Lie on your back with knees bent and flex your spine and come up with your hands touching the knees.
2. Lie on your stomach and raise your neck and upper back to look up.
3. Wall Bar exercises both in lying on the stomach as well as on the back are very helpful. You can slowly increase the number of the wall bar you are holding.
4. Lie on your back with your knees bent and your palms on the floor behind shoulders, elbows forwards and press up to raise your back.
5. Cycling would be beneficial if you can strap your legs and do.
6. You should also do some breathing exercises to keep your lungs expanded.
7. You should do exercises for the arms with dumbbells or weights and wrist strengthening exercises.