The workshop has a couple mods that increase mob HP/Dmg but that's all I would suggest. Seed doesn't have much impact on difficulty, it's more about how you play the game.

As others have said, playing without portals or map would make it a challenging and arguably better playthrough.

The rest of the stuff is basically avoiding mechanics / cheese that dumb down the game. Digging trenches / towers to kill bosses or spending the whole game kiting and shooting arrows isn't going to be much of a challenge but those sort of tactics are mentioned a lot around here for some reason.