Hey, I was just up at Big Lots here in town to look around and see what they had. They had several furniture items that might be handy in a skoolie. Mainly couches and mattresses. They have a real nice, full size micro-fiber couch for $325. I was planning to try and build one in my skoolie, but it would probably cost me more than that and I couldn't do as good of a job.
Also, they have good deals on mattresses. They have twin size mattresses that are made for bunk beds. They're around 6' long and 3' wide. Basically, it's a 5" piece of foam mattress that's attached to a piece of plywood. It would be pretty easy to cut it smaller if you needed to. It also has a sheet wrapped around it that's closed up with a zipper. That mattress was $50. They also have Serta pillow top mattresses that are $99 for a twin. I'm thinking that I'm going to go with something like this for my bunks rather than cut up the mattresses I found on the side of the road. Anyways, if you have a Big Lots near you, you might check it out.