There is hidden setting for the cursor size. You can change it using the console command:
/Console cursorSizePreferred -1
and change the number to find what works for you.
-1 will autodetect based on your resolution setting
0-4 will set it to varying sizes, 1 being the smallest
The first time you try and use a script command, you’ll get a warning about running scripts. As long as you make sure you only run scripts from trusted sources, you’ll be okay. (The one I posted came from this blue post here.)
There are also addons and weakauras out there to add stuff to the mouse pointer to make it easier to keep track of. I don’t use any so I can’t make any specific recommendations, but they are out there.