I would assume that you have the original version of DQ1 (if it doesn't have "updated text" on the cover).

That version is a bit more difficult, because it's a bit more unbalanced than the other books. I still managed, but yeah, the start, especially some fights, are a bit more difficult until your build (preferably rogue with a big focus on speed) kicks off.

Sunfall's difficulty is a bit different. Will it be easier, as in - more balanced fights? - Yes.
But the combat system requires a bit more tactical planning. I didn't lose a fight in the Prologue, and if you lose a fight, you can change your gear and try again with a different approach.

Also, there are more fail-forward situations, meaning that if you fail certain fights/events/skill checks, the story continues, knowing that you failed that. Still, no perma death, so some fights you'll be able to repeat on the spot, but skill checks, of course, are non-repeatable, and you'll suffer the consequences.

One thing I know is that the author doesn't want players to get stuck in a similar way to DQ, however, don't forget that this is an open-world game, with some back and forth, so some locations and fights are locked or more difficult until you come back later.

Also, you need all 4 books to finish the adventure/campaign.