Shell, I don't know what I would do without our swing/rocker/seat combo. We have abouncer but its really only good for when she is awake as if shes asleep and she moves a little it bounces and she startles. The rocker we have turns into a stationary seat which is the best I can rock her to sleep if shes cranky and then lay it back for her to sleep.
I probably wouldn't go the sofa, but thats because I take her outside with me in her seat and I prefer to know she is a little way off the ground. If its just for inside though it'd be great, as long as they can't roll off onto/into something hard when they start to roll.