"I currently have an HP 1080p, 27” monitor. I’d like something better, with better (read, more space) resolution with the same size."
Wait.
Hold on a minute.
You didn't tell us WHICH Mini you have.
The only way you'll get "better resolution" on a 27" display is to buy a 4k monitor and then run it in "scaled mode" to get 1440p.
(or at "full 4k")
But be aware that running any display in scaled mode is going to put a lot more work on the Mini's integrated GPU. It could slow down the Mini and heat it up, as well.
You could just run it at "full 4k resolution", but text
will be so small at normal font sizes, you'll need a magnifying glass to read it on a 27" display.
For "more resolution" that doesn't run in scaled mode, you might consider a 32" display with native 1440p resolution. Something like the HP "Omen".
A list you could check out:
IPS Monitor List: Best AHVA, PLS & IPS LCD Displays