What you need:
-Poison, Health, and Stamina Pots
-Flatten the Ground with Hoe
-Iron Mace (fully upgraded)
*unless you sort of "cheat" and get Silver early on for Frostner, that weapon will kick his ass.
-Iron Sledge (for random enemies)
-Stamina Foods (Muckshake)
-Shield optional as you should dodge all Bonemass attacks instead.
-When Bonemass pukes, do not run away from him, run behind and past him a bit, he will miss.
-Dodge all his attacks, pretend he's just a stinky Troll.

He's not terribly destructive to the environment either so building some barricades walls or floors should help.