Keep your tv disconnected from the internet completely like you did, and get a dedicated android box like the nvidia sheild for example. You can pick these up second hand for cheap.
Then uninstall any apps you do not require from the Sheild and you should be okay.
Now if you hold your own 4K media collection on a NAS you can install something like Plex and/or Jellyfin and keep your Nvidia Sheild completely offline only to access your local content. Though this really depends on your desired threat level or privacy level.