This achievement can be completed in Assisted mode and I recommend trying it with Claire's A story. I'm halfway through a playthrough myself and it isn't half bad considering I have a grenade launcher when using Claire.
I wouldn't recommend picking up ANY healing items throughout the playthrough so there is no accidental usage. This means all herbs and also first aid sprays.
Assisted mode also grants you aim assist, so aim around a zombie's/boss' head and it should automatically aim a headshot for you.
And finally, I would definetely recommend giving this video a go. I take no credit for it as it isn't mine but the person who did make it managed to beat the game (Claire A, Assisted) without using the item box, any recovery items and did it in less than 2 hours AND in fewer than 14000 steps. Use his guide if you need these achievements too.
Good luck!