I'll second the rec for "Cold Comfort"--in fact, I was going to rec it myself, but you beat me to it! ^_^ Normally, I don't read much Snape fic outside of Snupin, but I heard good things about this one, and it turned out to be an amazing story. The ghost!sex was, as you said, incredibly sensual, and I loved the Slytherin-ness of the Baron.