We have previously explained the main conditions with regard to women’s clothing. Please see the answer to question no. 6991.
There is nothing wrong with what you mentioned of wearing a long, loose white coat over your own clothes.
Shaykh Ibn Baaz (may Allaah have mercy on him) said: What is required of female doctors and others such as nurses and workers is to fear Allaah and wear modest clothing which will not show the shape of their limbs or ‘awrahs, rather it should be moderate clothing that is neither too loose nor too tight, and that will cover them properly in the manner required by sharee’ah and will prevent the causes of fitnah. End quote from Fataawa al-Shaykh Ibn Baaz (9/427).
And Allaah knows best.