One thing that you really might want to look into are the variant rules that start at page 263 in the DMG. We use the Gritty realism rest variant on 267 and lingering injuries on 272. I've edited the table of injuries for my own game, and created a second one. It still needs more playtesting.

Basically, I have two charts. One for each critical hit, and one for when my players fail a death save. I do make the effects stack, and it may get slightly expensive to have them removed.