Is there anything out there comparable to my original Kindle Oasis? Mine has lived in airplane mode its whole life and I’m afraid for when it finally dies

Boox Go 7 (B&W version) or Boox Page (discontinued) if you're willing to go Android. Both have the Oasis form factor with two physical buttons. Battery life is more like 1.5 weeks but hasn't been an issue for me at all. For me, I wanted Android after my Kindle to use the same apps I use to read books (or saved articles via self hosted Karakeep) on all my other devices.

I've never found one.

Kobo has the Sage which seems similar at first glance, but unfortunately it also has a stylus. It's closer to a Kindle Scribe or a Remarkable device.