I've spoken to Joe. He will not fit a single shock absorber, only a pair. So that's nearly £1200 plus labour.
I will be getting the PFS kit for £450. With her low mileage and only occasional long journeys, so, unlikely to be a big issue..
I don't have an issue with the Bilsteins. The 9-5 is notorious for getting through rear shock absorbers. The Hirsch ones were from Sachs and they lasted about 50,000 miles. I kept them on long after that, and the replacement made me realise that I should have done it a lot, lot sooner.