I live in an old house with horsehair plaster walls. One of the walls in my living room has a large crack running the length of the wall. It appeared after someone sat on the sofa with a little too much enthusiasm and pushed it into the wall. I've tried repairing the crack but because the wall is now "squishy", the plaster can now be pushed in without much force, the crack reappears the first time anything touches it.
My question is, can I drywall right over the existing wall without much hassle? Or is there a better way? If this is the best/easiest way to fix this, how do I make the joints between the new drywall and the old, like the ceiling, look correct?