Critical damages/crippled limbs should *not* be possible to fix with restoration magic or potions, or the idea serves no purpose whatsoever. Magic and potions may give you a temporary means to ignore, but would work better (again) if magic was not regenerative. If anything it could be a mid to high level survival perk - a mage might not want to spend a lot of time investing in that skill just for that perk.
You get one attempt on patching up yourself which you may often fail at lower levels, but if you do it (even failures count) often enough, you may get the perk for free. You may even find it in a perkbook which is not in a known place, but in one of many possible places. Maybe you'll never find it? A risk you take on by not going for survival. Crippling need to be on top of any stat system.
Rewamp sleeping too. Healing from near death shouldn't be a one hour nap. A rest should go by with days the same speed as hours does for waiting.
Good case: 3 hours to heal + 3 hours to get well rested for 10% damage using own mansion bed and no crippling.
Bad case: 16 days to heal +12 hours to get well rested for 80% damage using dungeon bedroll and 5 limbs crippled.
So even the rest menu should have options (rather than yes or no), like:
* Sleep until healed (usually checked, or default).
* Sleep until well rested (usually checked, or default).
* Sleep until rested.
* Sleep until sunrise.
* Sleep until noon.
* Sleep until sunset.
* Sleep until midnight.
* An info box that shows what your stats will be at end of currently selected option.
* And now, finally, the sleep or cancel buttons, maybe a "save default" one too for quicker overrides.