And then... the old Woody Allen "Everything You Wanted To Know About Sex..." movie involving one of those "mad scientist" scenes in which Lily Tomlin is doing one of her schticks and is introduced as one of the doctor's crowning achievements... implanting the brain of a boy scout into the body of a telephone operator. I shudder to think of the possibilities.
For fans of Robert A Heinlein, there is "I Will Fear No Evil" in which a cross-gender brain transplant occurs and an old gazillionaire gets the body of a sweet young female. Then "he" discovers sex all over again but from the other perspective. (Some say that at that stage in his career, Heinlein had started down the road towards being a randy old goat, so maybe this is understandable.)
And as to the idea of body harvesting, it is done now for many parts including kidneys, corneas, and certain other transplantable parts. But there is a science-fiction novel series set a couple of centuries in the future involving a character known as "Gil the Arm" (based on transplants, of course). I forget whether that is Larry Niven or Jerry Pournelle, but it was one of those two who was the author. Anyway, Gil lives in a society where they bemoan the HUGE number of penalties that involve loss of some limb as a way of paying your debt to society. One passage sticks with me ... losing an internal organ if caught jaywalking on any federal highway.