Even with a maximized window on each monitor, my mouse slips right over into the other monitor without any delay. I don’t see very well, so I have trouble finding the mouse cursor easily. The two monitors are not side by side.
Can you recommend any way to fix this?
There’s no edge resistance for the pointer itself, unless moving a window between monitors.
One thing you could do is maybe have something which indicates where the cursor is:
@FreedomRocks, a new feature CursorBarrier was added to fvwm3 (you can find it in the main branch on github) that allows you to create barriers to keep your mouse from moving across monitor boundaries. You could set up a CursorBarrier on each monitor to prevent the mouse from moving from one monitor to another, and then use WarpToWindow on the root window to move the cursor between monitors. The new option is documented in the manual page.
Note, You will need to install the development libraries for the XFixes extension and build fvwm3 with meson to use this feature.