What to wear as a bra under my dress?

My prom is in 3 weeks and I need help figuring out what kind of bra to wear with my dress. The dress is backless with only criss cross really skinny straps and the back is low. My bust is a little on the large side I am a D to be exact. Please help me and suuggest products that you have used and know work or products that a relative use but you have witnessed work. Also provide links or stores were I could find the product. Thank you again any feedback is greatly appreciated !