Is it the fraught or crumbling relationships your readers are after? Veering slightly closer to "women’s fiction" than true suspense, plenty of books focus on relationships without sacrificing narrative tension.
Maybe it’s the claustrophobic nature of the tale, the unknown predator, or the violence underlying the stories? After all, it’s not paranoia if everyone really is out to get you. I find that horror novels like Josh Malerman’s Bird Box are a pretty good fit for the fear and claustrophobia, while others emphasize resourcefulness, survival, and even the effects of loss.
The appeal could also be a genuine interest in the weird workings of a broken mind. There are plenty of books that delve deeply into a character’s descent into mental illness or the aftereffects of trauma.
For me personally, I came to the genre through Gothic fiction (well, that and Tana French and Gillian Flynn). For those not familiar with the atmospheric stories of dilapidated mansions and their aristocratic residents, usually with a female protagonist (just like in psychological suspense) – well, they’re in for a treat. A GX Gothic fiction search, along with some judicious limiting, should serve these readers well.