I think i3 is now my lightweight window manager of choice. It’s really fast on very old or low powered machines, and I’d really like to try it on something more powerful. There is a learning curve though, but the documentation is great:
https://i3wm.org/docs/userguide.html
Commands that I use deserve a blog post, but basically it’s ALT+D to open programmes, ALT+ENT to open new terminals and ALT+2 to open/go to extra desktops.