In my opinion this might do great things for both immersion and difficulty balance. Me and my friends would be ever greatful to anyone who would make an injuries mod.
Knocked down = 1 injury status with corresponding debuff (con/dex/movement/hit chance etc). Stacking. Restored by Long rest.
I feel it is a big issue that getting knocked down has no consequence, that careless play is always instantly fixed with heals and potions. We use various difficulty mods, but when a bonus action AoE heal nullifies one or several knockdowns each turn, the odds are too much in the players favor. And it's bad for immersion that a character can get knocked down five times in a fight, and then continue with no consequence.
For reference Pillars of Eternity has a pretty good injury system
https://pillarsofeternity.fandom.com/wiki/Status_effects_(Deadfire)#Injuries
Knocked down = 1 injury
2 of the same injury = major injury
3 or 4 injuries = dead
Could maybe be added that the 3rd injury = small permanent ailment,
Would this be easy to make?