For a comfortable bigger mouse you would probably look at a Deathadder (Either the New Chroma, which is just a RGB color update and nothing else, or the 2013 edition) or G400s.
These have the "bump" or somewhere that your palm can rest on, so I would recommend these as top choices.
As someone said, Rival has the same sensor as the FK1 so you might be interested, but it's quite the opposite; people find it almost too big.
Sensei raw for the minimalist ambidextrous mouse like the FK1, but a bigger size.