Hi! You should *first* learn why your patrons are experiencing difficulties with a traditional mouse in order to choose the appropriate mice for them. Otherwise, it's like trying to guess someone's shoe size over the telephone. (For example, is it the shape of the mouse cupped by the palm, the size or location of the buttons, etc. If someone has arthritis, certain hand and finger positions and movements should be avoided, such as ulnar deviation, which some mice promote.) See if you can consult with an Occupational Therapist--they specialize in these things. The OT association website in the US is at: http://www.aota.org/.
Best of luck,
Tanya