Have you played with basic layout like line spacing, left justified vs full justification, increased spacing between paragraphs etc? There’s pretty good data that all of those increase readability and reading speed by giving you more features on the page to anchor on.
I’m not visually impaired (not more than the average for my age anyway) but I saw a significant reading speed and comfort increase when I implemented all of those recommendations alongside a comfortably readable font. I imagine they’d work well with Open Dyslexic or a hyperlegible font too.