Windows 10 lets me select normal, large, and extra large, but even the largest setting looks quite small on a small high-resolution display.
Is there a tool that could help make the mouse pointer even bigger?
There are several options, besides increasing size, to improve visibility of the mouse pointer. My favorite is to make it 'inverted' so that it is white while on a dark background and black while on a light background. See this link for details on how to do it.
You can also show mouse trails, which help to see where the mouse is when it is moving; instructions available at this link.
You can have a blinking circle appear around the mouse when you hold down the Ctrl key; instructions available at this link.
If you really want a custom cursor Stardock's CursorFX does a great job. CursorFX has a number of built-in cursors, animated cursors, sound effects for your mouse clicks and lets you create your own cursors. There are also thousands of pre-made cursors for CursorFX available at WinCustomize.
If you just want a basic really large cursor you can try the xxl cursors available at rw-designer.