It's also worth noting that as long as you don't mind the overall difficulty, you can do the White Palace and the dream bosses without danger of dying. Some of you might not find the Crystal Guardian to be difficult (especially since he's been nerfed a bit in the Hiveblood update) but since we're already skipping one full mask there is no reason to fight him unless you want to skip a different mask shard instead. The game counts one full mask (4 mask shards) as 1% so all in all we are skipping the maximum of 12% with this plan.

Banishing the Grimm Troupe / Defeating Nightmare King Grimm (1%) The numerous tomes of my detefted art, And, in the hollow of this skeleton My soul inclosing, hither am I come, To tell the cure of such uncommon ills.

What exactly are we skipping here that would normally be required for completion?:

The dream bosses (dying to these wouldn't end your playthrough in Steel Soul mode btw).

Obviously, since we want to make this task as easy for ourselves as possible, we choose to ignore the argueably most difficult parts of the game:

Hollow knight steel soul guide