Springs

The last time I looked at building a couch, either I was rolling in money or the price on upholstery springs is insane. Unless I’m wrong, an upholstery spring is still just a loose coil of semi-rigid metal.
I adjust looked at done instructions for making my own springs, but I want terribly impressed. I’ll probably research it more myself. If probably do well to keep on looking for a super at less than autonomic astronomical prices. I wonder if my co-worker’s husband who does car upholstery has an idea?