Swedish auto lamps on ebay sells very nice leather bases for fairly reasonable price. they don't do the backs [squabs] though as they said the SIPS airbags are too much liability.

Check these out -

https://www.wetokole.com

Look at their selection, from mild to wild - not cheap though

I have the same problem with an 850. A few years ago I changed the drivers seat for $40 at the local boneyard, now it is going away too. There's fewer donor cars around at the boneyard and the leather is all getting too old, so that option seems gone

As an interim solution, I had a small tear, and repaired with clear silicone adhesive, that seemed to stabilize things. When I see a crack or opening I'll use that adhesive to delay the agony.

There are local people that replace furniture fabric that might repair seat covers. Something worth investigating.

Good luck, Bill