If your conference is about design, then I think that clothes should be only from outstanding and creative designers. I would probably choose something asymmetrical to emphasize the architecture and clean lines. Check out the clothing at https://doors.nyc/collections/clothing. There are very unusual options here from independent fashion designers. I often order things here for some important events in my life. Although, here you can find costumes for everyday life. By the way, I also advise you to pay attention to accessories. They always complete the look.