Currently, to my knowledge, the only difficulty adjustment is for the players reaction speed.
I suggest a slider that adds bonuses to the player character.
This would adjust the difficulty of all elements of the game.
These bonuses would be saved in the player character profile but would not be active unless the difficulty slider is set to an "active state" and adjusted off from default of Zero bonuses.
Just an Idea I thought I would pitch out there.
If there are other methods or variables that could be included that I did not mention speak up, comment, etc.