You're probably better off writing something so specific yourself.
However, even more potentially successful is talking to your significant other about whether they would consider the possibility.
Few options I can think of:
Head work - Can help you convince someone do as you ask. Should be done while the person is sleeping. A skull figure candle is best for this. Talk to it and convince him to propose to you.
Marriage spell with two figure candles - you can use a ring symbolically as well.
Calling upon spirits of loved ones to help you get your will.