Upholstered couches are generally built on wooden frames and covered with upholstery. The cushions and arms are often stuffed with foam. Over time and with regular use, an indentation may appear in a couch. The sunken area can become uncomfortable, making the couch unusable. Fortunately, there is a fix for sunken couches and it doesn't require the owner to be a furniture repair technician. You'll need only a few items to restore your couch.
Take the cushions off the sunken couch and set them aside.
Move the couch away from the wall, if applicable, and turn it over to inspect the frame. Find any breaks or cracks. If none are present, look for compressed springs.
Turn the couch upright and use a stitch remover to pull the stitches out at the back of the seat. Roll the upholstery from back to front, letting it dangle over the front of the couch, exposing the springs.
Measure the sunken area with a tape measure. Put on safety glasses and cut a section of plywood with a circular saw to fit into the sunken space.
Lay plywood in the sunken area and place foam padding directly over the plywood to make it soft.
Stretch the upholstery back into place and stitch it to the back of the seat with a needle and thread to finish. Move the couch back into place and put the cushions back on the couch.