A more sensible (but expensive) suggestion from me - have you considered airbag suspension? This would give a 'pan scraping stance to allow the infirm to climb over the side, but could be raised for normal driving and jacked up to the max for speed bumps. Worth a look, the youtube clip below shows that it's so simple even a three year old can work it, so long as you don't give a sh*t about their health and safety...
http://airride.co.uk/
http://www.youtube.com/watch?v=60aiAfSP0hg