Replacing the Springs on an Old Couch?

I have a 65-70 year old couch, that has been in the family since I was little. I am attached to it, but my kids think I should get rid of it and buy a new one. I can't afford that, I just want to repair it. It sags alarmingly. I think I need to replace the coil springs as well as the s shaped springs. Is there a video or book with instructions for this? I had it reupholstered about 10 years ago, so it is acceptable, though it could use it again, but that will wait till I have the money.

By Greg F.