What sort of things does he like?
Ds preferred fact books to read to himself (thankfully, because "The Spitfire is mounted with 4 machine guns and the engine is..." is totally boring to read). So he went through a lot of WWII fact books and animal fact books. The best thing for him was taking him to the library and letting him choose. When he'd chosen them he'd read them very determinedly, so read far harder books than I would have chosen.
Frog and Toad books are great for that age, because there aren't many words per page, but they're decent stories and, as you say, chapters which makes a child feel they're really reading "proper books".
I used to have a book called 365 stories. I wonder whether he'd like that sort of thing. They were all short stories but I loved being able to read one per night.
Some of the younger Enid Blyton's like The Faraway Tree/Mr Pink Whistle, even Adventurous Four are good for that age. If you can get the old Dean versions they're big print and have nice line sketches throughout.
If he likes fairy type things then you could try him on Rainbow Fairies. My girls loved them. Ds was unimpressed when persuaded by his sisters to try "When Jack Frost appeared, it was almost interesting" was his beautiful review. He didn't want to disappoint his sisters.
The "boy equivalent": "Beast Quest", which he did love, although were dreadful reading out loud, are really slightly older than Rainbow Fairy, although if you can get him into them, there's about 10 million (well, I think about 150 really) of the same story written slightly differently each time, so no shortage of them.
What we did to encourage reading was they had lights out at 7:30, but if they wanted to read quietly until 8pm, then that was fine, and if they were quietly reading, I sometimes wouldn't "notice" until 8:30.
Although I think dd2 still did plenty of research for her book "101 ways to read after lights out" which included an A&E trip after one attempt....