but we have Wyze cameras. I don't know how big ours are but maybe they have small ones. Ours were not expensive.

We have one for our grandson here at the house and I think you will find an array of prices. And it has volume. Our gives temperature etc. Pretty cool. It’s small and we monitor from our phones.

and research Consumers Report for reviews.
I find them very helpful.
Just took their advice on a new mattress and sleeping great now.

If it's just to check up now and then, the simplest one you can find will do.

I actually found a wired one at the thrift store (that is kind of rare). Perhaps something like a baby crib monitor will do.

Fancy "critter cams" will have storage for X amount of time and wi-fi connections. My neighbor has one to see who's been cruising the grounds. Probably motion-activated.

I just avoid like crazy any camera (you know their names) that sends data off-site. Any data sent outside your home can and will be used against you by other people.

I read the tech news and in the past week or so, breaches have happened at Dicord, the UK foreign office, and the Northern Ireland Police ... described as "monumental"

There's a review of crib monitors here that should give you an idea of the options. Some use wi-fi, which could put you out of range. One uses a signal (like a little tv transmitter), and so on.

https://www.babylist.com/hello-baby/best-baby-monitor