Replying to...
I want to be in full control of my mind, so that when another takes control of my body–perhaps putting me in prison, perhaps torturing me–my mind will not give in.
Studying stoicism might help, but while I'm tempted to say you need Satan, I recognize that that imagery might be off-putting. All the same, I would suggest that quiet, enduring, intransigent DEFIANCE is an oft-overlooked virtue. It certainly isn't one you'll find encouraged by the culture around you; the powers that be prefer us obedient and malleable, rather than adamant in our belief that our lives matter and obdurate in our refusal to live in any way other than that we've chosen for ourselves.
Nevertheless, defiance was the fire Prometheus stole from the gods to give to humanity.
Or, if you prefer a bit of false gospel that I've been using in the worldbuilding materials for my Starbreaker saga...
For Helel so loved mankind that he yielded his place before the throne of the Most High to become His Adversary, to teach us defiance by his own example and quietly endure damnation as the price of his lesson.