Wunderlich do one, built on the standard seat pan, but with less foam. Damned hard, so I sent mine off to Melvyn Hunter for gel pads, but didn't like the result much.
So, tried a Sargent seat, in the low version, which uses its own seat pan, and is very comfortable.
Just got a second hand Corbin, not gone far with it yet, its not a 'low' version, but seems to be narrower at the front, so getting feet down not too tricky.
Will do some more miles on it, then decide which one to keep.
HTH
Shug 29" inside leg