I find that if I try to beat the enemies in combat I very quickly gain so high sadism that my pleasure skyrockets, even from just a single fight. Is there any way to reduce or counteract this? Either reducing sadism, reducing pleasure gain or decreasing pleasure.
Endurance reduces pleasure gain directly.
Having higher resist (via accessories/titles/mind skills) can lower the pleasure damage taken from other sources, but not sadism related pleasure.
And by resting at the 2nd floor toilet, you can lower fatigue (high fatigue --> lower stats --> increased pleasure gain, among other bad things) and by masturbating there also, you can reset your pleasure to 0 without ending the day.
The toilet side job does however come with risks, as you'll start getting passives and prisoners will start sticking their dicks through the glory holes.
My advice, other than noting everything I wrote above, is to keep fighting through the pleasure. Get Healing Thoughts and start having sadistic orgasms.