You can also use a black background behind your "floating subjects" and then cut them that way. The most important aspect of this excercise is to have the camera in the exact same position when you move the couches and other subjects out of the room. Otherwise, the perspective will be off. Even a few inches will be noticible to the human eye, since it is very keen to these differences.
Example: Use a black backdrop in back of the subjects, and also under them. You will need also to put these black drops on all sides and anywhere else you want subtracted from the frame. All your doing is masking with black backdrops, just like you would do in Photoshop, but with real materials. After you get everything masked off, take the images. Now, make sure you do not move the camera at all. Remove the couches and backdrops and retake the images. You now have two sets of images ready for compositing.