New
#11
You can get USB Track pads for PC Perixx PERIPAD-501II Wired USB Touchpad - Multi-Touch Support for Windows 7, 8, 10 - Scrolling Feature - 86x75x13mm: Amazon.co.uk: Computers Accessories
Not really sure it would help with a shoulder problem though, have you considered going mouse left handed? Can be done with a bit of practice. I can use one either way.