Secondary Monitor to purchase

Hardware and technical stuff
1

I currently have the following as my main monitor:
Acer XB270H Abprz 27-inch Display Full HD NVIDIA G-SYNC (1920 x 1080) Widescreen Monitor

I would like to get a second monitor but not sure if I should buy a new primary monitor and use the above as a secondary.

My price range is about $300.

Any suggestions?

2

Typical set up is buying a better monitor (4K maybe) and then setting up the old one in Portrait mode for easy PDF reading /web browsing. I don’t have this set up though because my old monitor, a Dell something or other, is not able to be turned vertically. I chuck it into a store and bought an ultrawide monitor to replace it.

3

Walmart have the HP Omen 27" for $350 right now if you can find them in stock.