More literal:
* Furaha ya maisha yangu: This directly translates to "joy of my life."
* Furaha ya moyo wangu: This means "joy of my heart," adding a more emotional aspect.
More poetic:
* Upendo wa maisha yangu: This translates to "love of my life," implying the person is the source of your joy.
* Nuru ya maisha yangu: This means "light of my life," emphasizing the person's positive influence.
* Utamu wa maisha yangu: This translates to "sweetness of my life," signifying the joy they bring.
More specific:
* Utamu wangu: This means "my sweetness," implying the person is your source of happiness.
* Furaha yangu: This translates to "my joy," directly stating the person is your joy.
Ultimately, the best translation will depend on the context and the emotion you want to express. You can choose the option that feels most fitting for your situation.