I want to keep the original leather intact, and I've got a hunch that my problem can be tackled from underneath, so I turn the chair over and remove the bottom cloth. The webbing has disintegrated and with nothing supporting them, the coil springs are running riot.

I cut away all the webbing and staple new strips in place. Next, I tie each spring base in three points using a curved needle and jute string, so they are firmly held in place and can work as a unit again. I use one length of string but I suppose the knots could be tied individually.

The seat is plumped up and the chair comfortable to use again. This is a great way to salvage an old armchair and to preserve its top cover.