the game is designed for you to spend time to fully upgrade each time before the boss.
The elder, you are expected to have a level 3 fine bow or bronze weaponry and fully upgraded armor and shield, as well as good foods made in a cooking pot and making use of the best ingredients you can get at.

That said you can cheese many of the bosses with good movement skills and a bow. You can rush the content and do it in not upgraded gear, whatever you like. The less effort you put in, though, the harder it will be, and while you can make up for that with skill (esp 2nd+ playthrough) it isn't recommended.

If the first boss killed you, you are not ready. You may even want to gear up a bit and do him again for practice (and a cool looking head trophy) before you go looking for harder fights.

Be sure to make use of all you have. If you beat boss 1 you can now make a pick, which is critical to progression...