Hi,
Any healthy, well-balanced diet will do you just fine. Lactation is a pretty nifty system and even malnourished mothers are able to sustain their babies with breast milk - though they'd no doubt be better off with more and better food. If you're on a restricted diet, or lacking in certain minerals, etc, then you may want to talk to your health carer about supplements.
I would be very wary of taking breastfeeding advice from Weston A Price.