We haven't had a TV in over 20 years so I have absolutely no idea what I'm doing.
Something right, for sure!
I have a fingernail understanding of what a "smart" tv is vs. a "regular" tv. I think (?) we want to get a "smart tv", right? So we don't have to get any type of add-on products in order to stream?
It's easy enough. If it's on sale now, it's a Smart TV. It will, depending on brand and details, report everything you do on it, including things that aren't done internally (like what DVDs you watch with an external player, what video games you play, etc) upstream. Some of them have cameras and mics that can safely be treated as "always hot," and likely to stream a lot of what's going on in the room they're in out to the internet, because... big data analytics. Or voice activation. Or something of the sort.
If you're fine with all that, get a random Smart TV from the past few years and it'll be fine. No need to really worry about LCD vs OLED vs etc, it's not going to matter. A cheap 1080p TV in your desired size will be totally fine.
If you're
not OK with that sort of data collection and analytics, get something, don't connect the TV to the internet, and get a cable to let you connect your laptop to the TV as an external monitor. It's less-bad, that way.
Roku is particularly bad about "exfiltrating all the data they can if you let them touch a network." Their "privacy" policy is a laugh, it basically says, "Anything we can do, we will do. Anything prohibited by the laws of the country we collect the data in will be solved by moving it to another country first."