For a challenging playthrough I like using the seed "Irongate"

The Boss stones (starting area) is placed on a very small (meadows) island. Far enough from mainland, that it requires you to build a raft to be able to reach the rest of the world.

You start off secluded and cut-off in a small bit of meadows and everything you would normally be seen, in a meadows, can be found there.. and the Boss stones of course.

Once you manage to scrape together the materials to build a house and a raft, you have to decide the direction you want to sail... The closest, most obvious shore is immediately met with Black Forest, or go the opposite way, and a very LONG raft trip to get to Eikthyr Altar.

Sail North from there to find the Merchant, in a rather peculiar spot.

Great map where nothing is handed to the player, and even locks the player into the starting area until the player can craft their own freedom from it.

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.

The vanilla game can be played in quite challenging ways; perma death, no bosses, no map, no portals or any combination of these.

And by doing the above you will find most random seeds will work fine and in no way will reduce the self imposed challenges.

If you have played the game through at least once (all current bosses) and have a good understanding of how things work then I would suggest a 'no bosses/no portals' run.

You can just Google for interesting/unusual seeds. I've seen a few lists with funny/easy/challenging generated worlds.

There are maps that can be somewhat more difficult due to situations like described in the post that you found, but there are multiple locations for each boss, so another solution could have been to find an alternate location. That adds a little bit of difficulty, but not much.

I suggest making the game more challenging by turning off portals and turning off the map. Both of those significantly increase the challenges, and (IMO), make it a more enjoyable game.

The downside of both of those is that it's going to take longer to "complete the game" if that is your goal, but if you are looking for something that is slower paced, and will likely get you into more difficult and challenging situations, I think it's a good fit.

sadly the game has too much "cheese" dont want your house raided. raise/lower the ground. cant haul meterals and ore through portals? logout to temp world drop everythign into chest... go through portal in your main world. then go collect your stuff from the alt world. (my friend does this and its pisses me off)

the difficulty in the game is very difficult to adjust without mods. honestly you should look into some mod reviews on Youtube because THAT will greatly extend your experience in the game regardless of seeds. just avoid the cheaty stuff. some things people make is just gross. plus playing the game with your kid. heck yeah that's a blessing i always wish i could have done with my old man! that alone is the best experience.

this is my favorite seed
All Bosses & Trader Seed: bXUnvqrUHs

if you use the Better Continents mod available at nexus Mods using the Vortex Mod loader provided there. the seed takes on an even more incredible experience. but whether its vanilla or modded this seed hands down is the best.

honestly if you host via a dedicated server, a group of friends can use this seed to create a rather nice society in the paradise world of Valheim.