You don't have to actually buy from this site - but definitely worth using.
https://www.pcspecialist.co.uk/
It will literally ask you step by step what you want to buy, so power supply, GPU, CPU, monitor etc., it will then tell you what will and won't work together, recommend changes to make it run smoother etc... Then, if you don't mind spending that bit extra, they'll build it, stress test it, overclock it and install OS and send it to you meaning you just plug it in and go..
But like I said, you don't even have to buy from there just use their build your own PC form and see what'll work