Bigger X11 Cursors suitable for 4k screens

The default X11 cursors are quite tiny when the display is a 4k screen. How can I use bigger cursors? Requirements: * Must work under plain X11 (no KDE, Gnome or similar bloat) * Should have at least a bigger root window cursor, i.e "arrow" * Should work on FreeBSD I have looked at the Xcursor(3) manual page which talks about the ~/.icons directory but I am unsure which files to place there and how to activate them. I have a bunch of directories on the system, such as /usr/local/share/icons/oxygen/64x64 /usr/local/share/icons/oxygen/64x64/categories /usr/local/share/icons/oxygen/64x64/apps /usr/local/share/icons/oxygen/64x64/devices /usr/local/share/icons/oxygen/64x64/emotes /usr/local/share/icons/oxygen/64x64/mimetypes /usr/local/share/icons/oxygen/64x64/emblems /usr/local/share/icons/oxygen/64x64/actions /usr/local/share/icons/oxygen/64x64/places /usr/local/share/icons/oxygen/64x64/status /usr/local/share/icons/oxygen/48x48 /usr/local/share/icons/oxygen/48x48/emotes /usr/local/share/icons/oxygen/48x48/devices /usr/local/share/icons/oxygen/48x48/apps /usr/local/share/icons/oxygen/48x48/mimetypes /usr/local/share/icons/oxygen/48x48/status /usr/local/share/icons/oxygen/48x48/emblems /usr/local/share/icons/oxygen/48x48/actions /usr/local/share/icons/oxygen/48x48/places /usr/local/share/icons/oxygen/48x48/categories /usr/local/share/icons/oxygen/48x48/animations each of which containing a large number of icons as *.png files.