A little tip regarding all bosses.
When i go fight a boss i build a small house at the edge of the boss biome.
Example if its in the swamp i build it 100m outside the biome and put a teleport inside so if i die i can fast teleport there vs having to sail.

Another tip if you die then when you respawn you can run in and grap your gear in the swamp and run away and at a safe distance wear your gear again.

Regarding bonemass, then yes he is weak to frost damage.. But that is also a bit of a problem since you can only get the required things to build them in the mountain biome with the snow.. And that is a dangerous place to be for many reasons such as you are not really strongg enough to fight many of the creatures there, so blund weapons are what you need.
I actual belive before you summon bonemass you could technical speaking build some defensive wood spikes and maybe that will also damage him or at least make him slower.
Its also a very good idea to drink an anti poison drink.

Another tip.. in the swamp you are pretty safe if you build a house up in the trees.
( i dont think you can put the teleport up there, but try ).
Use this house to store supplys and if you build in a house near the water you can sail there and load things up fast and get out of the swamp biome.
Do not leave your ship unatended in the swamp the leeches will find it and sink it
You can make a wood wall out into hte water and so to speak keep them away but in general dont leave your ship in the swamp ;-)