Deaths Door at 0HP: When someone falls to 0hp or less, they get to make a save vs poison/death. Fail the save and you die. Make the save, and you live one more round. Continue making a save each round until you fail one and go to meet your makers, or until someone takes time to stabilize you (1d3 rounds to bind wounds, 1 round to cast Cure Light Wounds or force a Potion of Healing down your throat, etc). After that you’ll make it, but need to recover as if you've just been brought back by a Raise Dead spell (1HP, 50% of movement and suffers from chronic weakness for 2 weeks; no spell casting, combat, or any other strenuous activity).
Adventuring at 1st level can be pretty deadly; this is just one more tweak to help make survival slightly easier.