Last week, I was laying in bed in the middle of the night thinking about projects as I sometimes do and I remembered that we had an old toddler bed upstairs in the attic. I knew I could rip it apart and Frankenstein something together. I had some 2x4s and some 1x4s and left over paint. Good as gold.
(not my photo, but same bed)
I decided I wanted the couch to sit a bit higher than the standard toddler bed so I marked 1 foot to the bottom of the 2x4 and drilled holes for the metal slats. After adding arm rests and a back rest, I added some diagonal supports on the sides and a couple additional horizontal supports across the front and back.
(from the back you can easily slip a large basket for blankets and one deflated bean bag)