There are a handful of supplements that can be helpful for depression,but they do run the risk of causing mania. The ones I know of are St. John's wort, 5-htp, and SAM-e. I'm sure there are more. I was scared of them because I do get manic on antidepressants. Now I take 5-htp. The first few weeks I took it I felt a bit hypo, but that has leveled out over time. It's a good option for me.
My suggestion would be to take them supervised. Tell your partner or whoever is the most tuned into you and your behaviors. Have them let you know if you are falling out of character.
Other things that help me personally are fish oils, LOTS OF WATER, exercise and b vitamins.
And weed. Praise the great state of Oregon for allowing me to self medicate openly. *works well for depression but is TERRIBLE for mania... Use caution