I'm not sure what ur exactly looking for, but i've recently purchased an Asus ROG Z390-F motherboard in combination with a Intel i7 9700KF.
But if your looking for less CPU power you might wanna look into a 9600K for example.
EDIT. Sorry i didn't see you mentioned AMD.
For motherboard you could look into a : MSI X470 Gaming Pro Carbon
And for CPU you might wanna look for a 2600X or 2700X or you wait a few more weeks for the 3000 series. It's up to you.
Simple answer: get a 2nd gen Ryzen 5. Its the best bang for your buck for gaming, and you'll have an easy upgrade to a 3rd or possibly even 4th gen Ryzen 5 or Ryzen 7 in the future. Theres nothing signicant you'll lose by skipping Intel for gaming, but you'll gain platform longevity and a big wad of cash that can be put back in your pocket or reinvested into a component that actually matters (like a GPU).
I really don't won't to buy a new case because my atx motherboard doesn't fit since the io shield is so big any ideas on how to fix this problem. My case is Cooler Master HAF 912, motherboard ASUS b450-f.
First gen Ryzen are the best bang for buck. R5 1600 can be had for $80 at microcenter or $116 online. These chips will overclock up to 4 ghz (3.8-3.9 about guaranteed). Any B450 will work with any Ryzen cpu (including the updoming 3k series).
The hyper 212 with the FX 8350 is good for about 4.5 ghz (used one with a 8350, 8320, 8310 and all hit 4.5 ghz easy). My Ryzen 7 1700x x2 and R5 1600 all do 4 ghz with a Gammax 400 cooler (same basic performance as a Hyper 212).