The mouse is not the most accessible device for users. Double clicking or single clicking can cause strain on your fingers. It is also hard to move the mouse if your hand has problem with finer motor control.
One inexpensive alternative is to use a joystick. Using software, you can set the buttons on the joystick to match the button actions of the mouse.
You can try, http://download.cnet.com/Joystick-To-Mouse/3000-18541_4-10170790.html. I haven't use this software. The one I used, phatsoft, is not available now.
One trick is that after you connect the joystick to the computer you may need to add it in
Start/Control Panel/Game Controllers and then calibrate it.