Try this Life on for Size

At the beginning of your upkeep, if you have 50 or more life, you win the game.

Cumulative upkeep (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.) When this enchantment enters, you gain 20 life. When this enchantment leaves the battlefield, you lose 20 life.

If you would gain life, you gain twice that much life instead.