Anyone know if you can "retrofit" a lumbar support to Audi seats as I can't seem to find anything on the net. If not, any reconmendations on a decent lumbar support you can fit to your car seat? I have the back of an old man waaaaay too young!

You can get slimline Mackenzie rolls which will fulfil the role of a lumbar support quite nicely. Look'em up and see what you think. Physio med is a good place to start. They're only cheap, from memory.

Stick a rolled up towel behind your back.

Or you know those foam floaty sausage things for teaching kids to swim – get one of those.