If somebody is still interested in discovering good fonts for KOReader: STIX.
https://www.stixfonts.org/
I like them, they are intended for printed book (with Math fonts too) but works well also in KOReader and they are freely available. With large KA1 screen it seems to read a "real" book.
Edit: not only for printed book, from the stix's site:
"The STIX Fonts have been designed to work with all web browsers, word processors and other scholarly communications software, as well as all general purpose software."
"Most of the glyphs in the STIX Fonts have been designed in Times-compatible style"
May be the best times-like fonts ever.