I know you said you ruled out Onyx but I would actually suggest giving that a second thought. My spouse had a Kindle Paperwhite and switched to the Onyx Boox and really likes it. The construction is very similar to a Kindle but you aren’t stuck in the Kindle environment. It also has fantastic battery life (like most eink readers). Since it runs Android it works with basically any e-reader app you might want to use, she consistently uses Google Books and Libby and they work great.
I know you said you ruled out Onyx but I would actually suggest giving that a second thought. My spouse had a Kindle Paperwhite and switched to the Onyx Boox and really likes it. The construction is very similar to a Kindle but you aren’t stuck in the Kindle environment. It also has fantastic battery life (like most eink readers). Since it runs Android it works with basically any e-reader app you might want to use, she consistently uses Google Books and Libby and they work great.