Designing on the couch is great with a paper sketchbook and a pencil in your lap. My second choice would be a tablet with a pen (iPad Pro with pen, for example). Very free-flowing.
A traditional notebook/laptop/desktop/etcetera - Nah, doesn't work that well. I tried it myself, but it is too finicky and awkward in my opinion. Designing with the mouse or Wacom and keyboard is best done on a sturdy desk while sitting in an ergonomic chair or standing (standing desk required).