As one who likes Corbin seats a lot myself I decided to try a different solo seat this time for my Road King for two reasons. Corbin was a lot more expensive plus for my model the seat has puffed up stitched ribs which I didn't care for and they said would not make one w/o them.
C&C seats came highly recommended on a Harley forum so I called and spoke with them. They said their foam varies a little but is firmer than stock but they would be glad to use one of the firmer blanks for me since I like Corbin seats. I was a little nervous ordering a seat that I'd not sat on or even seen, from a company I'd only just heard of. Long story short I ordered one in plain vinyl actually they suggested using two slightly different textures which I did, it arrived in two weeks and I couldn't be more pleased how nice it feels.... 100% more comfortable than the stocker. The best part is it's only $255 vinyl, $295 leather. Even allowing for additional shipping to the UK it shouldn't be too bad.
http://www.ccseats.com/RoadKing.htm
In case you didn't see this thread it has a picture.
http://www.ukgser.com/forums/showthread.php/387669-New-Seat-and-Windshield-On-the-RK