I think I would take a different route, because big randomness isn’t fun for me.
Have you played Fate? It’s very good, and free. It has “stress” that’s kind of like hit points, but it also has this idea of “consequences”. When you take a hit but don’t have enough free stress to cover it, you can take a consequence instead. Stress is easy to recover, but a consequence sticks around until you get treatment.
As I said, I don’t really like big randomness. In Fate, it’s always up to the player if they want to take a consequence or not. Sometimes the alternative is the character just gets taken out. But if you do take a consequence , it’s up to the table to negotiate what it might be. Fall off a ledge? Could be a broken leg. Got stabbed? Could be an infection. Bothered by a ghost? Now you have a fear of the dark.
To port this over to DND , I’d add three “consequences” boxes on the sheet- minor , moderate, and severe. Each one could be used to soak one hit. The minor one could be 25% of their hp, the moderate 50%, and the severe 75%. When you take a hit that’s less than the box, you can mark the box instead of it going to hp. Probably tweak the numbers a bit since I just made those up. If you want to be even harsher, lower the max HP some, too.
This probably would be a mess, but I started typing it out and don’t want to just throw it away.
But I do recommend looking at how other systems do stuff for ideas, and stealing them
Also make sure your players are into whatever ideas you’re pitching.
I think a lot of people don’t get good information and then don’t connect the dots when they do.
There’s a lot of slop and mis/disinformation out there