Hi OP, I found this while searching for the same answer, my DD is 9 soon and I wanted to get her an e-reader. I have the cheapest kindle, which has a built in light, and I've never really seen how the paperwhite is worth the extra expense. So was initially planning on getting the same for my DD.
But recently I've been having a lot of issues with Amazon, deliveries rarely showing up, not being able to get much on short delivery, prices always being more expensive than other retailers, them charging me for subscriptions I didn't sign up to and then making it extremely laborious to cancel them etc and I've decided to withdraw from Amazon as a loyal customer, I don't want to be tied into Amazon for e-books forever. Some of the books my DD likes are only on Kobo and not Kindle too, and anything not on there can be found online as a PDF.
Also I hated the free kids content deal on the fire tablets, I found it overwhelmed my children with choice, and the book content isn't that good on there, so the draw of the free kids unlimited content isn't for me either. We have recently taken to going to the library regularly, and upon learning that Kobo is the only way to borrow e-books I decided to go down that route.
Not all libraries still use Overdrive, so it might be that yours has changed to Borrowbox. You can check what service they use on your council's website. Mine uses both Overdrive and Borrowbox.
I've gone for the Kobo Libra 2 for my DD, which is more than I wanted to spend, but it was the cheapest one that had USB-C, and that was important to me. Plus it can be held landscape, and you can use buttons to page turn as well as swipe. I thought this important as my kindle is swipe only and often it mis-reads swipes and can be frustrating to access settings because of this. I want the reading experience to be as simple as possible so as not to put my daughter off. It also has the blue light filter.