If you are happy with the paperwhite and your only complaint is the battery, then get a newer paperwhite. They usually improve the screen brightness and performance with upgrades, so I’ll stick with the devil you know.
I tried the Oasis 2 years ago and returned it. I did like the form factor or buttons on it. If I remember correctly , it did auto-rotate text , which was nice.
I went back to my paperwhite ( 7th gen, 2017 ) and I’m happy with it.
This thread prompted me to check out the currently available PW and Oasis kindles.
PW is on gen 10 ( 2018), but I don’t know what improvements were made over mine.
Oasis on on Gen 10 ( 2019).
What surprises me is that they haven’t updated them in a while, and both are still micro(or is it mini? ) USB connectors. The next versions of both should have USB-C , but who knows when they will be released.