Hi Lorian, Welcome to Cruise-Chat!
Congrats on booking your first cruise.
Not to be all technical, it really does depend on the class of ships about the sofas though. Also some of the porthole cabins have sofas, but they are not single convertible ones for sleeping. There are a few Category 5A cabins on the Conquest class that actually accommodate 4 guests. Those tend to get snapped up pretty quickly.