“Outside, Inside” by Gila Manolson. I recommended it in the past to another poster who bought it on my recommendation. Based on things that you’ve written, I think it’s right up your alley!
You might also be interested in “The Magic Touch” by the same author. It’s about being shomer negiah, but she writes a lot about tznius in general.
Her books are not about the halachos – they are meant to develop a love for tznius.