I know nothing about plants, I rather have a tendency to kill them even when reassured they NEVER die. I killed a cactus, FGS!
But, I am willing to try again, after 15-20 years of safe distance.
I am thinking of putting 3 plants on the sills. No idea which plants like humidity/not a lot of daylight (well, there is daylight, but not a lot, frosted windows), it can get quite hot. I need to be able to move the pots easily.
My bathroom is not huge, but it is spacious, steel grey and white. There's nothing on display (deliberately), modern enough and quite clinical. There is no splash of colour anywhere, white towels at all times. I prefer it like this, but I think I could cope with a bit of green.
The windowsills are quite wide (30 cm) and the three windows are large and say 1m high, maybe a bit more, no blinds or anything, just frosted glass.
Could you suggest a plant that would thrive in such an environment?