Steam Big Picture is very couch friendly, if you're using a game pad and what you're launching supports a game pad. That's why it works for a couch gaming PC. Firefox has pretty bad gamepad support last I checked.
It's been a while since I've had to customize it much but I believe the Steam overlay allows you to map controller inputs to anything, uniquely for every given app you run through it.
That said, at some point I think yes, you just get a bluetooth mouse/keyboard to go with it.
