Death, Dying and Resurrection

Detailed Justification for These Changes

I dislike the 5th edition system for handling the process of a character dying. While it is certainly simple, I find it doesn't effectively protray the evolving tension of a situation where someone is dying. It is merely dependant on random die rolls which do not take into account the severity of a character's injuries, their declining condition as they continue to move closer to death, or their natural constitution abilities which help them persevere and survive. It also removes the incentive for maintaining a high HP total, and rewards players for saving their healing spells until a character is dying, instead of healing injured characters, which does not make sense to me narratively. Additionally, spells like Healing Word effectively break the death saving throw system as they allow immediate rejuvination from 60ft range as a bonus action, regardless of the character's current condition, or the amount of healing performed. This is tricky because Healing Word should not be nerfed, it just doesn't fit with the death system of 5th edition. Pathfinder (D&D 3e) has a much more involved system which handles this situation very well, so I like to adapt its ruleset for D&D 5e, while adding one final phase of dying, which I call Falling into Death's Door.

I find the pathfinder death system gives more opportunity for characters to prevent a PC death, while also making the process of dying feel much more tense and realistic when compared with the 5th edition system. It also fits much better with certain spells and class features like a Paladin's Lay on Hands or the spell Healing Word.
Disabled - If you reach 0 hitpoints, you are considered disabled. You are not immediately dying, but gain the staggered condition. If you decide to perform a standard action (or any other action the DM determines to be strenuous), you take 1HP of damage, fall unconscious, and begin dying with an HP total of -1.
Dying - You are considered dying whenever you have negative hitpoints (i.e. taking 5 damage while on 3HP will cause you to start dying at -2 HP). While dying, you must make a DC 10 constitution saving throw, with a penalty equal to your current negative HP total. On a failure, you take 1HP of damage, on a success, you stabilize at your current negative hitpoint total. A natural 20 on this roll is considered an automatic success, regardless of the current penalty. Any characters taking continuous damage automatically fail this check (i.e. from a poison or a bleed effect). A stable character does not need to make this check.
If your total negative HP meets or exceeds your constitution score, you fall into Death's Door. You must make a single death saving throw (DC 10 d20 roll, no modifier added), if it fails, you die, if it succeeds, you regain 1HP. A natural 20 on this roll will result in the character immediately stabilizing, returning to consciousness at 0HP, but being considered disabled (as previously described).
If you take damage from a single hit, which drops you to negative hitpoints equal to half of your maximum hitpoints (or consitution score, whichever is higher), you are instantly killed, without the opportunity to save from Death's Door.

Stablization and Recovery - While dying, any form of ranged healing (i.e. a Healing Word spell) will only heal for half of its normal amount. A dying character who recieves any form of healing immediately stabilizes at their current negative HP total. If a character with negative HP (either dying or stable) recieves healing bringing them to an HP total of 0, they regain consiciousness becoming disabled. If this healing brings them to an HP total above 0, they regain consciousness becoming fully functional, but remaining prone until they take movement to stand up.
Another character can use an action to stabalize a dying character with a DC 15 medicine check, taking a penalty to the roll equal to the character's current negative HP. Using a healer's kit removes this penalty and lowers the base DC to 10. A healer's kit has only 3 uses. The Spare the Dying cantrip behaves identically to using a healer's kit, and gains a range of 30ft.

Resurrection

After a character has died, it is possible for them to be resurrected. Doing so requires powerful magic and has a chance of a failure should the soul be unwilling to return to the body. The only NPC characters capable of resurrection spells are very high ranking priests and clerics, who can cast revivify. More powerful resurrection magic is very rare, and usually only the highest ranking priests of a religious order are capable of perfoming it.
When revivify is cast on a dead creature within 1 minute of the creatures death, the caster may perform a skill check to attempt to aid the process of reuniting the spirit with the body. This usually entails an action personal to the dead character which embodies the essence of their nature, and thus helps to bring the spirit back to the body. But any action which can reasonably be argued to aid in the process of resurrection may be used. Should this check succeed, it will add a +3 bonus to the resurrection roll.
The DC of a resurrection begins at 8, and increases permenantly by 2 for each occassion a character is successfully resurrected. If the resurrection is performed on hallowed ground, the DC decreases by 2. If the resurrection is performed on desecrated ground, the DC increases by 2. Additionally, a modifier will be added to the roll for each level of the spell slot above 3rd (i.e. casting Raise Dead will add a +2 modifier, while casting Revivify at 4th level will add a +1 modifier).

More powerful resurrection spells

When a resurrection is performed using Raise Dead, Resurrection, or True Ressurection, a full ritual takes place allowing up to three contributions. Similar to the ritual with revivify, each contribution must in some way attempt to aid the process of reuniting the spirit with the body. Each successful contribution (determined by a skill check) will add a +1 modifier to the ressurection roll.