You might consider using separate devices for different reading needs, rather than one size fits all.

For general, mostly text reading (like novels), try using a regular smaller e-ink device. Things like the Clara, Kindle PW, and other B&W e-ink readers are really good at that specialized task.

For things with complex graphics or layout (like your PDF's, graphic heavy things, computer or scientific texts, etc.), I think you're better off with a larger, higher resolution display, and I prefer color for this usage. So, even though I don't want to needlessly pile up extra devices, I find I really need 3 devices on a regular basis:

* Phone, general purpose comms, light computing and web access.
* Clara HD, e-reader for mostly text articles, and fiction.
* 13" laptop (one could also substitute a large tablet, something like a MSFT Surface, and Ipad, etc. here) for the PDF or complex graphic usage. The advantage of using a laptop for this is then you don't need to own a large tablet in addition to the laptop and other devices. I've been able to get away with only owning these 3 devices, works great. My HP Spectre X360 laptop can be folded back like a tablet for viewing large PDF's and computer books with complex page layouts, its perfect for that. Although I wouldn't want to sit there holding that thing for like 3 hours like you would when reading a novel; light as it is, it's too heavy for that kind of usage.

ETA: Some people I know at worked have toyed with the idea of a 'tweener' sized tablet/laptop type thingy, which *would* let you in theory use it for both regular ebook reading, AND for tablet-style entertainment, AND for light laptop tasks, AND for larger PDF type viewing. In this scenario, the only devices you'd own would be the tweener device and your phone. Sounds good in theory, but I have yet to see a device that's ACTUALLY good at all those functions. The original Microsoft Surface tried to be--I own one at work, they're really nice as an ultralight laptop-tablet, but still WAY too big/heavy for extended ebook reading. The new Microsoft Surface Go is even lighter and a step in the right direction size- and price-wise, but immediately, it compromises on the laptop power and for my work at least, it would lack enough computing power to be a serious laptop. So, while I like the idea of a do-it-all 'tweener' device that's halfway between a laptop and a small tablet, I have yet to see one that I think actually does the job or that I'd spend my own money for.

Anyway, food for thought.