As a person who wants to see the beautiful device I own, Ionly use iPhones naked, plus in a pouch/sleeve when in my bag.
Senas Ultraslim Classic is as slim as it can get. I love their UC series. But here in Germany we have a very good manufactory called Fitbag. Their cases are similar to Sena Ultraslim, also not the same. Their cases are slim too, only a little higher, so that the device can't fall out of the case by mistake. They have a variety of material. Leather, cord, alcantara, normal material too. And on the inside they stitch off some microfiber material which cleans the Display when you put in and out. It's very good quality, esp. the leather cases. They have at least 30 different cases with different colors/material. All Made in Germany. Only the sometimes very slow delivery is on the negative side.