Price & Price certainly supports lottiejane about myrtle & hyssop and also indicates GERMAN Chamomile as well as caraway. All with plenty of clinical research.
I prefer to treat with calendula / marigold and evening primrose (30%) and NON cold-pressed sweet almond (70%). Note, that cold-pressed base oils would be less favourable due to higher pollen levels!
Also note that both caraway and hyssop make gorgeous herbal tea, but should not be used at all by pregnant women (emmenagogue) and should also not be applied or ingested too frequently as they both have very high levels of ketone toxins.
All said, myrtle and blue chamomile are very safe and gentle bets – blue chamomile in very small dose during first trimester, though