ikea bookshelf with reused futon - into great window seat! I could see putting casters on this too and making a rolling bench storage. Also, building this out of pallets and a walmart clearance outdoor cushion?
You don't need no stinkin' sofa! Put some nice fluffy cushions directly on the floor. Take that futon cushion off the frame and fold it against a wall. Add pillows and blankets. The options are endless!