Get leather armor, it's a good damage reduc for the 1st boss.
The first boss isn't really hard but more into testing what you know.
Just make sure you eat 3 different food before you fight him for maxiumn health + stamina. (You want to remember this for all the bosses really)

Knife is a nice weapon but it's designed for surprised attacks (knife's inflict more damage when enemies do not spot you when dealing the blow). You may find it a bit difficult to fight the 1st boss with it.

Also, Valheim is good indeed. For an EA game and its price, it's quite really fun for me and worth the bucks for me. I know there's a few really bs part that made me rage and frustrated before (like crashes and late game stuff) but eventually I kinda got used to it, it is in EA afterall, I hope they do get address later down the line (asap if--well, possible)