Skill level has a much bigger effect on success rate than willpower.
If you'd like you can go in one of the mageguild and have a spellmaker make spells you can cast with a good success rate.
Something like, Heal 5-10 on self, good to use out of combat, low mana cost and 100% success rate, will raise your Restoration level pretty fast too.
Oh and if you join the mage guild you can empty the Mage Guild's Supply Chest, contains restore magicka potions.
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