Was just thinking how much i want to do this, except not against a wall, so the table is fully ex posed and accessible. Adding a console table behind sofa doesn't take much space, and adds storage space to a small family room.
DIY Sofa Table - Buy a 12 inch wide piece of wood at home depot. Measure the length of the back of the sofa and cut the wood to match. Stain the piece of wood with some Miniwax Dark Walnut stain. To secure it to the wall, use "L" brackets underneath and screwed the wood into the brackets.