Pocket size ebook reader for carrying around

Hello,

I'm looking for a small-ish (5-6") ebook reader to compliment my current one (Kobo Aura One). I like the Kobo, it has all the features I like but the size is just too big for me to carry it around.

I'm currently looking at Pocketbook Touch Lux 4 / HD3 models. Wondering if I should spend ~ $200 on the same thing I already have, minus the large screen.

I would also like to install Koreader on it, if possible.

I'm looking for an advice here. Is there a better alternative (cheaper or more compact device that has a 5" or 6" screen with a thing bezel) that I should buy instead.

Thanks.