I succeeded in my goal and created a book that consists of reading text at the first-grade level, but also the combined text that is intended for a more advanced reader. I added braille to this text.
I made illustrations that contained enough contrast for the visually impaired but did not disturb people without a visual impairment. For the blind, I made a simplified tactile version of the drawings.
The story is about a cat named Ollie that searches for a home with his companion Owl. They do this throughout the seasons. The story is also made to get children to answer questions throughout the book and go into conversation with their advanced reader companion.
This version was made with what I could make myself, since printing book a book with braille is very expensive. The end result is therefore different from what I had in mind.