RED III said:
If you can still find one, I'd buy a 1080p TV as live TV does not look so great on 4K TVs. 4K TVs have 4x the pixels and the TVs processor is trying to stretch the image across the entire screen to make it fit. Live broadcast television signal is in either 720p or 1080i. I have both and live TV looks better on my 1080p TV. Just food for thought.
What kind of 4K tv do you have? What kind of 1080P set do you have?
The quality of the processor in the TV is going to drastically affect how an upscaled picture looks. Your blanket statement isn't true. Many TV's can scale content to the panel resolution and have it look better than a lower resolution panel could ever look.
The problem you will run into buying a 1080P tv now is that you are going to be getting the absolute cheapest panel, backlight and processor. You're basically going to be buying 3-4 generation old technology.