peasandcucumber - if your child has a diagnosed visual impairment, many UK publishing companies will provide ebooks of school reading books and textbooks to the school for your DC to use. The educational publisher I work for provides this free of charge. PM me if you'd like more info on this.
We've very recently bought DS a nexus to use as an e-reader as he has a visual impairment and enlarging the text really helps. He is Yr 3 so I haven't looked at levels as such but there are definitely some early reader type books.
One thing that has really frustrated me is the price, I bought The Twits on the kindle app and it was more expensive than if I had actually bought the book from amazon which I think is ridiculous and especially frustrating when we own two copies of it!!!