Custom Enchantments
I didn't remember all of the enchants, but some of the best enchants for boss fights on armors that I know:
1. Guarding: Reduce damage taken from bosses
2. Hardened: Increase Armor durability
3. Tank: Gives Resistance effect
4. Overload: Increase Health capacity
5. Drunk: Gives Strength effect, (but also gives mining fatigue and slowness)
6. Hulk: Gives Resistance (or Strength, I forgot) effect, (but also gives slowness)
The other enchants that also helps:
1. Enchants that gives fire resistance effect, I forgot its name, should be on Mythical or Legendary. You can do /ce to check the full list.
2. Implants: Restore hunger when running. (When I have this with nutrition on my sword, I almost never run out of hunger on boss fights).
That's all that I can tell, hope it helps.