systemd: how to setup desktop environment without display manager?

I’d like to completely avoid DM phase and run straight into desktop environment. Is there any systemd service for that?

All that is needed is to correctly restart Xorg when it is killed by Ctrl + Alt + Backspace and not restart it when it was killed by a crash or another measure. So any ready solutions would be greatly appreciated.

Notes on 19.04 and prior versions (in my particular setup):

  • Autologin is broken in LXDM.
  • Ctrl+Alt+Backspace is broken in LXDM.
  • SDDM is broken and doesn’t start.
  • Good user-friendly and nicely working KDM is gone.