Since historic clothing was often made to measure, finding a form can be very difficult. I have built my own in the past using PVC pipes and elbows. That way you can get the exact measurements you need. The PVC is then padded out with batting and encased in unbleached muslin to get the exact size. I have done similar things with very old, smaller sized dress forms too. I have had really good results in the past, and although the PVC will off gas there is a barrier between it and the clothing. I wasn’t able to find a reasonably priced mannequin that wasn’t custom made for our small size and didn’t need some sort of barrier added anyway.
You may also want to look at the child sized mannequins, and padding them out in the needed areas to simulate an adult.