Unfortunately, HP can't really be changed that cleanly. I made a topic about this before the patch, and most felt that IF is fine. Never thought about something like adding armour points, but I disagree with adding too much armour everywhere (including armour looms). A 34 pierce/blunt attack at 90 armour is similar in damage to 34 cut damage on 65 armour.
IF is pretty decent when grouped together, but point for point, it's clearly less important than other skills. I'd argue that some skill points are worth 3-6 points of IF, since most attacks in the game would deal more than 15-20 health.
I like where this is going, though, using IF as a source of damage mitigation, maybe something that's not stats related.