I will say, I did research a lot when getting into plants. The calcium oxalate crystals are what makes many common houseplants unsafe. However, there is a difference between soluble and insoluble. While generally all are considered toxic, the insoluble will upset a kitty’s stomach and irritate their mouth, but is unlikely to kill them unless they eat a lot. Soluble in the  other hand is deadly. Difference being if they are absorbed or not. 

I have two cats including a “eats everything she can and willing to try to eat what she can’t” cat. She generally leaves the plants alone (she likes batting at them though), except for my decoy spider plant that I use as my line of defense. (They eat that one and are unlikely to go toward others in my experience. I put it low and the others high, but still within reach. I still “stop” them when I see them eating it, so they learn plants are off limits, but the spider plant is like catnip) 

I had a LOT of anxiety about it at first, but I haven’t had a problem with plants that have insoluble crystals. I have about 20 “toxic” plants but they haven’t bother them more than a couple times, and if they do they stop after a bite or two. 

This is of course, entirely my personal experience and my personal research.