https://telegra.ph/%E5%8F%B3%E9%A0%82%E9%AA%A8%E8%A7%A3%E5%89%96-%E5%9C%96%E5%BA%AB%E7%85%A7%E7%89%87cliparea-11-30-131
The length of your gown should be about what you're most comfortable in, so try out a number of options and choose what works best for you and your style.