My car currently has some later Sport wheels on it with 275/40/20 tyres they’re in quite the need of a refurb and I don’t think the ride is as good as previous FFRRs I’ve had with the correct wheels on.
What are my options in terms of sizes and styles?, I think I read 18s won’t fit on a TDV8 but not 100% sure, are 19s ok?.

There should be a sticker on the body near the drivers door catch listing sizes and tyre pressures for each.

 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

19s are ok, they are fitted onto mine, although I am hoping to find a set of reasonably priced 20's

19” are Ok and are the stock size for the tdv8. Proper spec 20” are ok, not sport wheels, with 255/50 20’s. 19” do give a slightly better ride though on the taller sidewall of 255 55 19. There is nothing that can't be fixed with a hammer😜😜
FFRR 4.4 SDV8 Autobiography Santorini Black.
Fiat 500x 1.4 multiair Lounge 2015
2010 LR D4 Commercial 2.7 TDV6

Mine came with wheels like yours. I’ve swapped them out for some genuine 20’s with 255/55/20 Grabber AT3 and it’s a lovely ride with good kerb protection and decent grip in all conditions.

Change the tyres from 275/40/20 to 275/45/20 and the ride quality will be restored. The larger side profile returns the sidewall height to the same as the original 255/50/20.

Bin/sell the sport wheels and buy some new take off's from Duckworths with 255/55/20 and the magic carpet ride will return