We're using ValheimRAFT which has made the ocean very easy for us because the boat moves way too fast, and because we have a huge boat: https://thunderstore.io/c/valheim/p/zolantris/ValheimRAFT/#config

And although we can adjust its configurations to make it more balanced, do you guys have any extra mods to make the ocean more dangerous? Like extra or more dangerous sea monsters?

I started playing modern Valheim, and I super love it. It feels like having done some major updates to the game. So much extra free stuff and awesome stuff. The quality so good that I would have been willing to pay for a DLC that includes everything -- and the best part it's free!