I've got an Aeron and they're adjustable in height so I take it that, by mentioning that it's a size C, you refer to the width of the desk.
I have no recommendations but I'd be interested too. I simply use a wide desk and put my screen in the middle so I have plenty of room left and right both for the stuff on the desk and for my legs.
My Aeron is set up so that if I put my arms behind my head the chair "falls back". I considered the more recent Mira chair: it's back support seems great (I just tried it for a few minutes) but... I can't live anymore without the Aeron's "pellicle mesh" ; )
For my keyboard and mouse I'm using a big piece of felt and I really like it (a felt bridge table cover but I'm now considering buying the stuff used to make quality poker tables and cut it to the size of the entire desk, not sure how that would work).
