At that age and reading level my DS loved the Pippi Longstocking and Dr Dolittle books. He also really enjoyed all of the Oz books which are around that level. Books of Wonder has great reprints of the original illustrated Oz books. There are ~3 Pippi books, ~8-9 Dolittle books(of which DS read illustrated version of the first 3), and ~12 Oz books. Plenty to keep you occupied if any these catch your fancy.