Buy a piece of wood from Home Depot cut to the size of your couch. Stain it with Minwax dark stain (can get at Home Depot) or whatever shade you like. Let it dry overnight or longer. Attach it to the wall with four or more L-brackets and you are done!
DIY drawer organizer project ~ 48" wood laths super-cheap at Home Depot, & the store will cut them for you. So simple it's not even really a tutorial :-) Would also work to make a shadowbox to display small items.