I tried my best italian to see how much it would cost to go in (€8) after much confusion the rotund older gentleman gave a speil which included the price. (I couldn't see it written anywhere) The staff were extremely helpful once they realised I was with my partner who is a wheelchair user. A lady pointed him out (as he was waiting outside of the office, because he couldn't get in) the man then gave me two tickets and said 'free' we were amazed!
As it was quiet the lady escorted us around the ground floor. You have to cross a cobbled courtyard which might be tricky for independent chair users.
We then had to negotiate narrow glass doorways and deep (single) steps through the different sections. (3sections i think) My partners chair is an 18in seat in width.
Once the ground floor was done the rest if it was easy as it had a glass lift that took us to the remaining 2 floors all smooth wooden flooring. (power chairs will fit in the lift)
Although not especially religious minded, we found the artwork and statues amazing. it's very well spaced out.
I would check the opening times. There is also a disabled loo on the ground floor but we didn't use it so can't comment.
Worth a visit (especially if they let you in gratis! Oh and infirmiera is Italian for nurse ;)