Vanity

Hello! I started doing ballet a month ago (I’m 20 years old). I have X shape legs and flat feet (but very flexible, I have an amazing natural arch when I extend my foot). I was told that by 2 of my private teachers) but if I stand on the ground my feet tend to cave inside therefore I assume I lose stability. Is there anything that can help with it? maybe a list of exercises and a particular type of shoes that can help me? Please help Thank you for you time and advice Alex