• minimal Debian install, with no Debian Desktops selected

  • for more ultralight, don’t check “basic system tools”

apt-get update
apt-get install xorg
apt-get install fluxbox vim
  • edit ~/.bashrc
vim ~/.bashrc
  • append startx if we’re not in it already.
if [[ ! $DISPLAY && $XDG_VTNR -eq 1 ]]; then
  exec startx
fi
  • reboot
  • login via console
  • wait for your new lightweight DM to start

Sources:

https://wiki.debian.org/FluxBox#Fluxbox_Session

https://wiki.archlinux.org/index.php/Xinit#Autostart_X_at_login