plasma is probably the easiest DE to install. Simply install the group plasma. Then enable sddm and remove xfce and lightdm.
I haven’t tested it but something like this:
sudo pacman -S plasma
sudo systemctl enable sddm.service -f
sudo pacman -Rc xfce4 xfce4-goodies
Be careful and review the list of packages to be removed carefully. It is a clean install, don’t login to the xfce4 session. Instead log into the TTY and do it there. That should keep your home directory cleaner.