The couch will probably be nothing more than a couch, not a pull-out.
The pictures I have seen make it seem like a large love seat (or a small couch). Depending on height, you may or may not be comfortable.
I have heard that the pullmans are comfortable, though, even though they take up a lot of room when pulled down.
The best way to look at it at this point is know that you (or the other third party) will have a place to sleep. It may be a good idea to wait until you are on board and able to see for yourself whether you will be able to sleep on the couch or not. You may want to note that all the couches I have experienced on cruise ships seemed to have cement padding.