I'd tweak Stormonu's suggestions a bit. Saves should be used to resist effects, not damage.
Fireball should hit an area and deal 3d6 fire damage, Dex save to avoid catching on fire. Lightning bolt should streak through people instantaneously and deal 3d6 lightning damage, Con save to avoid being dazed. Thunderwave should deal 3d6 thunder damage, St save to avoid being knocked to the ground and hurled away.
Strength Saves resist physical force & restraint. Example: Entangle, gust of wind, thunderwave.
Dexterity Saves resist things where dodging, ducking, or diving can help. Example: Fireball, dart traps, pit traps.
Constitution Saves resist poison, dismemberment, pain, and illness. Example: Lightning bolt, stinking cloud, stunning fist.
Intelligence Saves resist illusions. Example: Phantasmal force.
Wisdom Saves resist madness, strong emotions, and confusion. Example: Cause fear, confusion, feeblemind.
Charisma Saves resist charms, compulsions, and effects that try to make you follow orders, rather than simply feel a certain way. Example: Charm person, dominate monster, suggestion.
What about things that suck your soul? I'm inclined to just go for the current "You take damage that reduces your maximum hit points by an equal amount, so no healing until X." Where X would probably be 'receive magical healing,' or perhaps 'spend a week purifying your body.'