What to wear for trying on wedding dresses?

I have two appointments Saturday at separate shops to try on wedding dresses for the first time! I'm really leaning towards a backless dress and already have extremely small boobs.. like cup gaping while wearing an A cup so I don't have any intentions of wearing a bra on my wedding day. I have a strapless bra I bought earlier this week just for my appointment though. Also I literally only wear thongs, idc if the lady sees my butt or boobs but is that appropriate? I'm basically just wondering what I should wear lol. Thank you!!