I don't know about other wms, but in i3, floating a window is just a matter of pressing super+space. Moving it around and resizing is very ergonomic as well, it's just super+left click drag and right click drag respectively. The really nice thing about the resizing is that you don't have to hit a tiny window border target with your mouse, super+right click just snaps to the nearest border of the window you're in.

My guess is that most other tiling wms would have a straightforward way to float windows as well.