One the most difficult things for visually impaired people is locating the mouse looking up to the screen.
Therefore enabling locate mouse
or locate pointer
give some extra visual attention (flashing orange circle/waves) after pressing CTRL. (difficult to catch in screenshot: on the left)
Xubuntu doesn't have this invaluable tool, and Ubuntu is too heavy for the 1GB, dual core old hardware.
Gnome has it, Unity has it, Compiz has it, Mint has it. Xubuntu/XFCE doesn't have it.
It is not about a bigger mouse, that helps a bit. Some flashing attention is needed.
Using high contrast theme.
If Lubuntu has it, I consider switching from Xu to Lu.
Best Answer
In Xubuntu go to Settings Manager - Mouse and Touchpad - Theme. There you can make mouse cursor size bigger.
Also you can download additional themes for your mouse that make viewing the mouse easier. See xfce-look.org. You may choose the theme by your tastes.
I think this one best suits your needs: DMZ with Yellow Background Multisized.
As for Lubuntu: According to its wiki site, PCManFM and LxPanel don't use the cursor theme, you will have to change the cursor manually. See here for more details: https://wiki.archlinux.org/index.php/LXDE#Cursors
And one more option: Install MATE environment on your Ubuntu, it is lightweight running on 512-MB RAM machine and has the mouse flash option you are searching.
If you want to have only one environment you can even download and install Ubuntu Mate version as a single OS (But note that is is not officially supported by Canonical).
https://ubuntu-mate.org/longterm/
After you have installed MATE environment you can set mouse flash:
See the link for details: Quickly Locate Mouse Pointer In Linux Mint / Ubuntu | I Have A PC.