Most promises fail because they're unmeasurable. "I promise to always love you" is lovely and completely weightless. "I promise to say the hard thing out loud instead of going quiet for three days" is a promise with a spine.
Use this test: could someone film you keeping it? If yes, it's a real promise. If not, make it smaller and more specific.
Aim for three to five. Mix the registers: one that's funny, two or three that are sincere, and one that's a little brave — something that acknowledges the hard parts of a long life together.
Start each one the same way ("I promise to…") for rhythm. Repetition is the one poetic device that always works out loud.
If you get stuck, the Promise Idea Bank in the Bonus Pack has thirty starters. Steal one and make it specific to you.