Guy with very bony hands chiming in here... I found this to be the best mouse pad: . 2-3x thicker and softer than normal. I actually turn it around so that it slants toward me. I use a Logitech M705 mouse, which is nice except for the scroll wheel which is a bit bouncy/laggy at times.
Three thoughts: DEFINITELY: No matter what operating system you have, there will be a Device Control area where you can switch the mouse's handedness. DO THAT. Your speed of entry will be improved, too, as you will not be switching back and forth between the number pad and the mouse -- your hands never leave the surface. As well, forget about the $100+ mouses -- the thing you're purchasing is a framework for the actuation buttons/switches. No matter how cool the framework looks (and across the dozen or so brands), there are still only 2 or 3 manufacturers of the actual switches. Aside from the junk mice, a $50 mouse has the same switches/sensors as a $150 mouse. Last, as a mouse pad, I use a $5 plastic cutting board from Target (I think). It stays in place, it reads (laser-wise) as flat, and it protects my antique desk varnish from the sweat which would bleach it out in a single summer. ("Ewwwwww!") It's so thin that the heat from my hand will warp it over a few months, so I periodically roll it up opposite the warp, and leave it behind a wall monitor, to "cure" back to flat. So, mark me for 2x$5 mouse pads, rotated as needed. ("Cheap bastard!") You betcha. Okay -- a bonus: if you have tendonitis/tendonosis, do yourself a favor and find some Glucosamine HCl (not the sulfate, but the HCl), and take one pill a day for 3 months, and WOW will you feel a lovely difference.
Try different things, e.g. use the other hand, Wacom tablet, vertical mouse, trackball, Apple track pad, and definitely more breaks. Also there is software tools like RSI Guard which reduces the amount of clicks necessary. Take this seriously. You could damage your hand and arm for the rest of your life. You may want to consult a physiotherapist. There are some good books about this like "It's Not Carpal Tunnel Syndrome!: RSI Theory and Therapy for Computer Professionals"
https://www.elitetrader.com/et/threads/leapmotion-armrest-included-lol.246204/ https://en.wikipedia.org/wiki/Pointing_device
I only use trackballs. Better to use your thumb to traverse the screen than your wrist (much faster in this regard). And humans are one of the few creatures with opposable thumbs, so why not take advantage of that ?
Can't recommend anything specifically but stay away from Logitech products. As of late they're part of project obsolescence, deliberately designing their products to fail after warranty. My mouse and keyboard, although cheap, both failed in about 2.5 years.
What you need is a mouse with adjustable DPI , i use logitech G302 , has a button behind scroll wheel with 4 levels of cursor speed . couple other buttons that are programmable that you may find handy . Best thing i ever got for my 6 monitor setup https://www.logitechg.com/en-au/products/gaming-mice/g302-moba-gaming-mouse.html
I have a logitech keyboard thats over 10 years old , replaced recently not because its not working , just starting to look a bit shabby . I actually bought the exact same keyboard i was that impressed , backlit , super comfy and durable Also add that its wired which for me is a must have