Here is my suggestion:
If you want to continue to have health replenished throughout the battle, go with leech seed. I find that this works quite well with toxic, magical leaf, and sleep powder.
If you want to heal a lot of health at once, go with synthesis. I find that this works well with a sunnybeamer set.
If you want to do reasonable damage and heal yourself, go with giga drain. I don't have a specific moveset for it like the other two, but when paired with overgrow, it goes up to 90 base power. That works well with stab and can recover quite a bit of health.