Jane Nissen Books has a website

Jane Nissen Books  publishes classic children's chapter books. Her large format volumes, with an illustration here and there, are lovely. Nissen, formerly of Penguin books, has amassed quite a catalog of reprints from the last two centuries of children's literature. There are names that may be familiar like Arthur Ransome, B.B. and Dorothy Edwards. There will be many more unfamiliar names.
Particularly for bookworms, Jane Nissen Books provides endless opportunities to read books on one's high reading level, without having to turn to adult fiction. Not that there is anything wrong with proceeding to grown-up books, but often the subject matter is unsuitable. Jane Nissen's list stretches out childhood reading far beyond the typical book list.
Mistress Masham's Repose by TH White is a good place to start. It is one of Terry Pratchett's favourite according to the website (www.janenissenbooks.co.uk)