Hi,
I originally set out to have both the foam upgraded and the seats recovered. I then decided to additionally have my newish R'N'R mattress recovered to match the rest. Nick from Comfortz Leisure offered a seat swap-out. I'll provide a politician's answer to the price - depends on what you want doing and what material you choose and any specific individual requirements. I don't know what Nick actually did to the foam but before the work - I could feel the sharp tin edges through the seat

and now I can't

With hindsight I should have chosen the mattress covers with a couple of stitched panels (but I'm not complaining). More importantly SWMBO likes the look.
I'd approached a couple of local upholsterers and they produced stunning portfolios of work done on prestige vehicles e.g. vintage VW split-screen camper vans retailing around £30K upwards. These guys weren't really keen on working on something so ordinary but they were keen to charge between £550+ to £1200+ for 2 front seats

. Nick was significantly cheaper and that included the 3 piece mattress covers.

Became a no-brainer.