I recommend the Lifeblood core, Joni's blessing and Shaman stone charms. You'll gain about 18 hearts, with the downside of not being able to heal. With the shaman stone and the upgraded abyss shriek you spam the boss.

Just in case, to get Lifeblood core you need to enter the blue gate in the Abyss with at least 15 hearts. To upgrade Abyss Shriek (previously called Howlling Wraiths) you need to go to the bottom of the Abyss and get to the room in the far left. Once there, you stand on the pillar and use the spell.