I'm not the best subject matter expert on 4e, I received advice to look into 4e for homebrew and it's been good advice.
You've probably read about +2 to hit on the forums:
One is a creature being "flanked" results in a +2 to hit for the flanking opponents.Flanked Defined+2 to hit "Combat Advantage"
Adding in "Combat Advantage" for high ground to replace 5e's Advantage, would be better for combat.
Another is the minion rule, it lays groundwork for more fluid combat balance. I love it for allowing me to control how difficult I want the encounter to be.Minion Rule
The last is I have a homebrew rule for critical hits. I got the idea from looking at how 4e handled critical hits.4e Critical Hit
They're all good options, so I became inspired to set a damage floor for critical hits. Where the players still roll double the dice, but the damage can't be less than the maximum of a normal hit.