If you want something in the same line, the natural step would be
Pendragon , Neo Prog as Marillion with a good keyboardist (Clive Nolan) who plays very much like Tony Banks in Genesis 4 men era.
From all their albums I would try
Masquerade Overture , probably their best, if I'm not wrong (probably I am
) Pendragon is one of the last bands to use good old Mellotron.
If you want something more complex than Neo Prog' you could try
Magenta , their only album
"Revolutions" is really good, like a mixture of Yes and Genesis with a female vocalist that sounds almost like Stevie Nicks (Christina Murphy).
Iván