Keith a solution for you might be to bring your own assistant for your child. This assistant would know your child better than anyone you would hire on a ship for a week or two. Plus they would be available at all hours.
I sympathsize with your dilema, but the reality of any ship hiring and having available a staff member capable of dealing with the different needs of the various special needs kids that would be cruising each week is pretty unlikely.
I hope you can find a solution that works for your family, I am sure a cruise vacation would be nice for you guys, only unpacking once and having the same room each night would be less stressful than some other vacations.. Good luck !