I came across this beauty a couple of days ago> Not seen it in the flesh but is does seem to fit your use case.
Specs
https://support.remarkable.com/hc/en-us/articles/11500455428...
I use a refurbished 1st gen sony xperia 10.1 tablet that I bought for £100 on ebay. It is very light and has good resolution but the screen could be a bit bigger. The big plus is it takes an sd card and also a portable s/hdd can be attached so storage is no problem.