There are some reports of problems with the Kobo Aura One’s official cover - specifically, some covers fail to put the device to sleep when closed. Kobo decided to put the power button on the back, so it is difficult to find a universal case that is compatible with the device. However, some iPad Mini cases work with the Aura One. Two features identify these compatible cases - first, is the use of elastic bands or flexible bands that holds the device (most iPad Mini cases come with a form fitting hard plastic casing). Second, a large hole at the back for the camera.
The Kobo Aura One is similar to the iPad Mini’s dimensions and, due to this, flexible elastic bands should work with the device. Further, as the device’s power button is placed on the upper left of the device, it matches the location of the iPad Mini’s camera and so it is possible to access the power button. As an example, I’ve found Belkin’s ‘Smooth Bi-Fold Case for iPad Mini’ to be compatible with the Kobo Aura One.