Niffelheim

Potions and Food both work for this. You can see what the stats are of the consumable item by selecting it (highlighting it) in your inventory. The Food you can craft will only give a maximum of +20 Health but there are items in the shop (specifically the sausage and the bread) that you can purchase that will give you 100-300 Health.

The higher quality Potion you drink, the more Health you'll get from it. You'll mostly be using the "Weak Potion of Health", "Strong Potion of Health", and "Thick Potion of Health" as you play through the game so you'll be making your way to 10,000 pretty steadily as you play. As long as your diligent about healing yourself whenever you need to/can, you should unlock this trophy well before you reach Day 100.

Note: Sitting on a throne and standing in a Firefly swarm does not count towards this trophy. You must physically consume something for it to count. If you don't have this trophy by the time you finish the game, bring some Health Potions into a Cave or Dungeon and stand in a poisonous cloud with the Health Potion active. Your health will deplete and regenerate while standing still. Just be sure to hit your controller every now and then because if it idles too long, the game will pause.

Once you've consumed 10,000 HP in total, the trophy will unlock.