What could be considered casual/modern sadly does depend on both your race and gender too. For instance one of the outfits I like to use, that has semi become what people identify me by, is the Poncho. On a lalafell the poncho looks "natural" but might appear too big and uncoordinated on a larger individual. As you can see in this pic I have of the Lalamon Starters. (Viridian the Grass type, Pelito the Water type, and Toki the Fire type, lol) Please ignore the murderous chocobo behind us, lol?

also the Hingan/Doman coat/jacket looks "modern/casual" on me but might look old fashioned on you since you'd show more detail.

I personally recommend finding individual pieces you think could be modern/casual, and then seeing how they can pair up. Don't forget to play with dyes as well. They help a lot.