Hollow Knight: Voidheart Edition

Steel Soul mode is unlocked after completing the game. This is a hardcore version of the game where you have one life and do not respawn upon death. This run will be done on a separate save file where you choose Steel Soul mode at the start and if you do die, the save file is essentially deleted.

Assuming you know your way through the game, this isn't really any more difficult than a standard mode run because you can pause and quit before you die, then restart from the last bench you saved at. Almost all damage in the game causes you to lose a single mask of health and only a few enemies/bosses deal two masks of damage at a time, so as long as you're careful when your health gets low death should be a non-issue.

To increase survivability, prioritize finding Mask Shards, Charm Notches, and Pale Ore for Nail upgrades. The Fragile Strength and Fragile Heart charms (sold by Leg Eater in Fungal Wastes) are particularly strong since their drawback is basically nullified because of permanent death.

The game has a total of 112% total progress, with 100% being from the original base game and 12% coming from content that was initially added through DLC/updates, all of which is included in the Xbox One version. You only need 100% on your progress, meaning there is wiggle room in terms of what you have to complete.

After destroying the three Dreamers you can get into the Temple of the Black Egg in the Forgotten Crossroads. Interact with the statue next to the bench and your completion percentage will then be shown in your menu and on your save slot.

For progress towards 100%, this is what counts:

Upgrades/Pickups (38% total):

Charms (1% each charm = 40% total):

Bosses (1% each = 17% total):

Warrior's Graves (1% each = 7% total):

Dreamers (1% each = 3% total)

Colosseum of Fools (1% each = 3% total

Godhome Pantheons (1% each = 4% total0

Since you don't need everything for this achievement, I didn't bother with the Pantheons or the delicate flower trip for the last mask shard and I only did the first two Colosseum battles as the third is annoying. Once I was at 100%, I killed the Hollow Knight and the achievement unlocked at the end of the credits.

The Hollow Knight wiki is a great source of information on anything specific.

These two maps helped me immensely, as well:
Basic map
Fully interactive map