I usually work with EPUB and then convert to AZW3 for the Kindle. I use the Hyphenate This plugin in Calibre which greatly helps with justified text.
https://www.mobileread.com/forums/sho...d.php?t=208534
Exactly what justification problems are you're having with LRF files? I don't really have any experience with that format. Doesn't the Sony handle EPUB? Or does LRF just have advantages over EPUB on that reader?
Here's an example of justified text on my Paperwhite: