Use i3 with GNOME Session integration for Ubuntu 18.04
This repo creates a new session in GMD3 called "i3 + Gnome". The requirements are gnome-flashback and i3.
apt install -y i3 gnome-flashback
make install
make uninstall
Everything should work out of the box. If you like to use nm-applet add exec --no-startup-id dbus-launch nm-applet to your i3 config file.