Bio identical progesterone is the most 'natural' if by natural, we mean, most like our own.
I'm on Femoston and may have to try another, but I am afraid of trying elleste duet or any of the norethisterone synthetic progesterones, because I hear of so many women saying it makes them grumpy or anxious, and in the past couple of years I have made a recovery from anxiety that was really traumatic. If I went on norethisterone, I would just be really worried aobut being trapped on it for a fortnight with horrible moods.
Some women succeed with it though, I just feel too scared to take a gamble and would rather just use utrugestan/micronised progesterone (bio identical progesterone)
Some women find that they cannot get hold of it on the nhs though.