"...Green Hills...." was the first sci-fi book I ever purchased or read ..... ..... it was the first my daughter ever read ..... and she recently asked me if I still had the book as she wants it to be the first her daughter reads .....
Actually, Green Hills was the title of a paperback compliation of short stories that cost either a quarter or maybe $.35 back then. They also used to print two books back to back for about that price ..... lots of Andre Norton animal-sidekick stories.
FWIW, I bought Stranger from the sci-fi Bookclub and may well have a first edition ...... gotta look for it soon.
Regards