I'd read several articles and posts indicating that Bonemass was a really hard boss. Maybe because of that I was overly prepared, but it didn't really seem that hard.
I had full upgraded iron gear (although bronze shield). Used iron club as my weapon.
I had medium health potions, minor stamina potions, and poison resistance potions.
I started by just running up to him and swinging away, blocking his melee attacks. I would back off when stamina was down and use a potion if it was available. Used health potions when they were available. Had to clear out the adds every so often. But mostly I just ran in, swung till my stamina was out, walked around until it was back, repeat. If my health was getting low I'd walk until I could use another health potion, but I think I only went through three health and two stamina potions. Just one poison resistance.
Overall not that hard. Killed him on my first attempt without even coming close to death.