I just bought a new TV for my basement. $599 at costco for a Sony 4K 65" smart TV. Couldnt be happier. TVs are super super cheap right now. I dont think you can really go wrong with anything right now.
I have a guy at work who installs home theaters on the side. According to him, OLED, which is the only major feature that $599 TV does not have, is only relevant at fairly extreme viewing angles. So…pretty much a non issue if it’s just you, a trainer, and a tv. Or, as in my case…90% of the time just me watching a movie solo after my wife/kid go to bed.