More Stable Saves (3.5e Variant Rule)

The Problem
Binding saves to only a single ability score is problematic. For non-casters, given their reliance on magic items, have to consider even more ability scores, whereas spellcasters, with their access to buff spells of various sorts, don't actually care much or at all. To make matters worse, this system basically says that clerics will always have better Will saves than sorcerers, which is plainly odd.

To make matters worse, the disparity between 'good' and 'bad' saves becomes unacceptably high towards the end of the progression. A difference of 6 points between them even before taking ability scores into account is poor, and when ability scores are added to the pool, it just makes a bad problem worse. In order to mitigate for this, increasingly more resources need to be spent by all characters (but especially non-casters) to protect their poor saves.

The Solution
Fortitude saves can add either the character's Strength modifier or their Constitution modifier. Reflex saves can add either the character's Dexterity or Intelligence modifier. Will saves can add either the character's Wisdom or Charisma modifier. In all cases, use the ability score modifier that would yield the best save, even if it means adjustment on the fly based on ability damage or buffs.

Additionally, all base save bonuses are now calculated as 1/2 character level. If a save is marked as 'good', it receives a +2 bonus. Note that multiple instances of 'good' saves on a multiclass character do not provide this bonus more than once.