epithet
Explorer
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Facetiously: You could just try hitting yourself in the face whenever your character is knocked unconscious. You seem to want an individual, metagame punishment for failure. Perhaps if you're not keen on actual pain, you could do something like buy everyone a pizza, or donate money to a charity. Or say 10 hail marys.
More seriously: Your campaign doesn't seem to have any consequences at all, and you seem to have no investment in the game at all. You said yourself: a TPK isn't worrying to you. Why not? Do you just not care about the story at all? If your quest is delayed by an hour, that should matter. If the party are TPKed, you should care that the bad guys won, and that their evil plans will come to fruition.
You raise an excellent point here. There is a big, big, BIG difference between consequence and punishment. Character loss is only one of the possible consequences of that character's death, and most of those consequences should ideally give in-game reasons why the characters should try their best to avoid death. When you start jacking with the rules to implement character loss as a punishment to the player for letting a character die, then you're just being an antagonistic DM - and that rarely ends well.