I plan encounters to be hard so it doesn't generally come up. I want to use Lingering Injuries, but got voted down by literally everyone in my group (I'm the DM, but I don't impose stuff that the party doesn't want to do).
Negative hit points can also work, but find a bit unwieldy for modeling death--death saves aren't any better, but its what the players are used to, so we don't question it for ease of use, considering it something like bleeding out, either from external or internal injuries.
If you really want to make it more deadly, take a look at the DMG, on page 267, and implement the Slow Natural Healing Variant, as well as the Gritty Realism Rest Variant. This means that you have to spend hit dice during a long rest, which is 7 days, to heal yourself outside of magic. It makes taking damage something to be avoided at all costs.