There isn't room in an Inside cabin on the Pearl for a sofa or loveseat. Instead, what you'll find is a bed that pops up from under another bed, with three beds side by side.
There's room, but this may not be the arrangement you're desiring.
Here's a photo for an Inside cabin, imagine the third bed between the two shown in this photo.
Of course, if your Inside cabin can sleep four, the third could use the pulman bunk bed, which is shown on the right wall on this photo.
Edited to replace copyrighted NCL image with a link to the original source.