Take into account, that the part looks a certain way because it's constructed a certain way. Figure out the underlying structure, and that will give you an idea of how to approach a design job like this. I know when you're 90% through a job and you're trying to hack the last 10%, you don't want to hear someone say back-up and start over, but the company you're interviewing with is a furniture manufacterer, not a Game developer, so they're not looking for a prop they want an actual design.
One thing you should take into account, SolidWorks doesn't do fabric simulation, so a lot of the form elements like the deformed shape of cushions pushing against eachtother and the fabric stretching over the batting-you're not going to be able to model those realistically. You'll have to generalize their representations somewhat.
Off the cuff, I'm going to recommend you model this couch as a multi-body part. Use the weldment tools to create an armature that you can add stuffing and padding to. For the padding you're going to make simple chopped cylinders that define how much bow the padding has and then use boundary and fill surfaces to skin over the padding. Thicken the surfaces to make solid bodies.
At that point, you can use the indent tool to remove interferences between overlapping bodies so that you get good intersection curves.
Now, if this company is infact, just looking for a general representation, there's a saying that I take to heart: you can have a crappy model and if you have good textures and lighting, your scene will look good, so before you dis on yourself, throw a fabric texture on your couch model, change the environment to SoftTent and render it and see how it looks then.
