>>Between A5 and A4 in size

Very expensive.

For $59 you can get M5PaperS3 ESP32S3 Development Kit (960x540, 4.7" eInk Display, 235 ppi)

https://shop.m5stack.com/products/m5papers3-esp32s3-developm...

Or you can get:

https://lilygo.cc/products/t5-e-paper-s3-pro

But these have 4.7 inch display.

You can probably hack and repurpose old e-readers if you can be bothered with the technical pain.

Soldered.com makes some really nice eInk dev boards, including one with a 5.8" 7-color display: https://soldered.com/categories/inkplate/color-e-paper/

This is great! Thanks!