Our current best solution for a shielded computer mouse is made with several layers of self-adhesive copper foil on the inside of the mouse shell. Externally it looks like a normal plastic mouse. The results it terms of shielding are very good, the pain in the palm and the fingers have disappeared.
This shielded mouse is made starting from a commercial product designed for right-handed people, however it can be used also with the left hand. It has an USB connector, so to be attached to a PS2 port it needs an adapter.
EMF emissions from computer mouse
First tests with shielded computer mouse