I play solo and so I try and max out everything I possibly can before I take on the bosses. By then they are relatively easy. I do admit, I have Valheim plus mod installed but the only "cheats" I have turned on are more forage items upon pick up (berries), all dropped items float, and no damage taken to my builds (since I am solo I don't have time to be rebuilding everything.) This set up gives me more time to focus on character development and preparation for my next boss.

My advice would be to make sure your current biome enemies are easy to kill before to take on the boss. Typically I make sure the biome is a walk in the park before I take on the boss.