A “smart” TV is probably never a good buy. Screens live for a long time. The current “smart” technology will be upgraded next year. So don’t buy a TV with planned obsolescence.
If you go used, make sure you get a monitor with HDMI input. The current external smart technology and DVD players will also connect with HDMI. Does your current PC have an HDMI output? Some older, and even newer, laptops only have VGA. VGA doesn’t included sound, but HDMI does.
Got the hdmi on every computer, that’s a couple of Windows 10, a few Windows 8’s.
Go with external “smarts”. We bought an Amazon Fire Stick with Alexa services.
https://smile.amazon.com/gp/product/B00ZV9RDKK/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
Amazon reduced the price from $99 to $39 this year making it a cheap way to try out smart technology with an Alexa capability, to boot.
We also got an Echo for Christmas and have been having fun setting timers for cooking, getting weather information, playing classical music, and general chicanery with the audio interface. It is quite sophisticated for being so cheap.