[Pajamaman]

For hardware, I suggest either a Kobo or a Nook. Both come in > 6". Koreader will run straightaway on Kobo. You need to install some stuff. You need to root the Nook. It's not hard and instructions are available on the xda forum. Also it's Android so you can install other ebook apps.

Edit. Apparently you don't want Android, so scrap the Nook.

Apparently the hardware spec of the new generation of Kobo is similar to Amazon. But obviously their not as sexy as the Oasis. But the Oasis is totally locked-down.