Is there a good spot to farm Health plants?
The medicinal herbs seem to occur everywhere at more less the same density. Possibly a bit higher near places where there are big fights. Nobody sells herbs.
Try to keep the bar full, and get the 'Herbalist' skill to double the size of the medicine pouch. Also Healer and Gatherer for faster healing and more resources.
Also don't forget the Health and Full-Health potions which heal quicker. Craft a larger pouch to carry more of these, You can buy these potions. Ypu can craft the health potions from rich / fatty / boney meat, so hunt animals and keep a stock of meat.