How creative do you want to get and where do you live?
First: If you read more PDF than anything, buy a tablet. None of the e-ink devices handle PDFs well.
Otherwise, a Kindle Paperwhite is probably the simplest out of the box solution.
I'd avoid the Aura Edition 2. The Glowlight 3 (if you live in the US) is a better piece of hardware for the same-ish price.
The Aura Edition 2 isn't bad.
But you can get an Aura Edition 1 on eBay for half the price and it has an SD card slot and a flush screen. I bought mine there and so have a few others here.
If you're willing to look on eBay,
you can also get the Glowlight Plus for $60. It's got a much nicer screen than the Aura Edition 2 and it's waterproof (not important to you, but not bad for free).