I'm want safe homeopathic choices to take for my nerves while breastfeeding and found aconitum napellus but i also read it can be poisonous?

Are no guarantees: Truly homeopathic "medications" are made by repeated dilutions, so that the ingredient is not really there anymore (just the "essence" of it remains). That means there should be no active ingredient left to affect one's body. However, that also implies that the homeopathic "medicine" should be pretty harmless, UNLESS some other non-homeopathic ingredient (such as some other chemical) was added.