The best privacy method is to completely disconnect the TV from any wired or wireless network, and like you suggested to use it as a dummy display with the Apple TV (or whichever your favorite media player is). So in that sense you could just go to Costco (or any major electronics retailer if not in US) and pick one that you like the image & price.

I guess I am more concerned about random devices at home that need internet to work yet I have no idea what data they send where.