I have heard it said that unless you are considering a monitor at least 65 inches in size, getting a 4K monitor is pointless. I tend to disagree. But I understand what is being said. At a sensible TV viewing distance of 10 feet, human vision cannot benefit from the extra resolution.
More important may be the monitor technology and not just the resolution. OLED monitors offer amazing dynamic range, but cost a fortune in TV sizes. New technologies are now offering "HDR" as a buzzword that may actually mean something.
Any TV worth buying these days will be lit by LED, but there are at least 3 different ways to do it. Direct lit is supposedly better than edge lit, but not necessarily. Edge lit can be just as good - if done right. What Edge lit offers are thinner monitors, if that matters to you.
I was initially impressed viewing photos on my sons 55 inch Sony XBR55X800B. This is a circa 2014 direct lit model. A comparable model these days might be the Sony XBR55X900E, which sells for $1200. The current "budget" 55 inch offering from Sony is the edge lit KD55X720E, which sells for $700.
A company called TCL is apparently making nice 4K tv's that are well thought of at a decent price ($830):