How can I gain resistance to piercing, bludgeoning, and slashing damage while in heavy armor?


I am theory-crafting a character that takes very little damage. I want to use the Heavy Armor Master feat to help with damage reduction from non-magical attacks, as well as the Battlemaster maneuver parry, and the Goliath feature stone’s endurance. How can I gain resistance to piercing, bludgeoning, and slashing while also using the Heavy Armor Master feat? I am most interested in answers that don’t depend on external sources, such as other characters and magic items, but I’d like to hear answers including those as well. Multi-classing is an option.