What's a good, sturdy little houseplant for my kitchen window?

Hens and chicks. Real easy to grow and pretty. They are succulents but grow very well.
https://en.wikipedia.org/wiki/Hen_and_chicks

Philodendron is one of the easiest plants in the world.

I immediately thought of African Violets because my mom did well with them, but don’t know if they’d have an issue with the chilliness.

Some of these are too large, but I like The Spruce and it may give you ideas..

https://www.thespruce.com/best-houseplants-for-sun-4147670

Indoor acacia tree or bush?

Begonia.

You should do Philodendron!

There is nothing more sturdy than good old plastic plants.

I have that the Chlorophytum comosum (Spide3r Plant) is one of the hardiest plants I have encountered for a houseplant.

It appears that it can survive virtually anything but it it a prolific propagator and constantly produces ‘trailers’ which will either continue to grow or can be reported somewhere else or even pruned.

The Spider Plant produces tiny white flowers, normally prior to producing their trailers.

^^ Thanks for reminding me of it! They’re great for hanging, too. I’m going to get one!