Where to get quality summer dress attire?

I'm 15 a girl and I'm going on a trip that requires business attire. The dress code says I can have dress, suit/skirt with a blazer and dress blouse and dress shoes for professional after. For business attire I can have khakis slacks or dress capris kneelength skirts blouses polls or a dress. And shoes with a heel. And then I need casual attire too. All clothes have to bee finger length and notops that are strapless or the sleeves aren't 4 finger lengths. So basically no fun. I would LOVE it if you could give me things to get along with places. Thank you in advance for helpful answers.