Looking to game on a monitor

Welshboy98

Hi I've been gaming for years primarily a playstation, and was an early adopter of 3d and then 4k. I used to be quite good at FPS games but in recent years I've become terrible at them.
Today I tried my friends 4k Samsung pc monitor which he uses his ps4 pro for. I was dominating leaderboards again.
Turns out the in put lag is so bad on some of my recent tv purchases it's been crippling my gaming without me realising.
I had an idea it could have been the tv's but I thought 0.040 to 0.060 input lag wouldn't make that big of a difference but it has.
So I'm now looking to upgrade to a desk and a good 4k monitor. I'm currently gaming 99.9% of the time on a ps4 pro and would like to know what monitors anybody would recommend around the £400 Mark.
I'm currently looking at a LG 27uk850 and the rest of that range the 600 and 650.