I've read that Calatheas are notoriously hard to look after, but I have has this guy for 2 years and it's somehow still alive and doing great. There are a few brown tips but it has doubled in size since I got it and regularly gets new leaves! (It's probably due a pot upgrade/split soon)
I live in UK so I don't think humidity even exists, and I only water it when I remember, maybe every few weeks (or a bit more regular in summer).
It was already a pretty mature plant when I got it - maybe that's the key!

I'm about to move and don't know if it will survive the long car journeys so I want to show it off now just in case, hopefully I'm not jinxing it...

fabulous! I'm jealous

You have done very well indeed! Some Calathea don't need the high humidity. This one, Calathea binotii, is one in lower humidity. But its a large grower, tops out at about 5-6 ft tall. It seems to be the smaller growers that are drama queens

Paddle leaf calathea like this one, Crotalifera (the rattle shaker) also can make it fine with less but it too is a large grower and more resembles a Stromanthe in the leaf blade morphology