I don’t know which book to get next. Can you help me ?

First time posting here, but I have been so frustrated trying to find a book that might suit me and I really really need to start reading again, so I figured it would be worth a shot.

I would like to read a classic piece about man and nature with some kind of philosophical twist to it (perhaps shouldn't be too long-i.e. 300-400 pages max). Books that I enjoyed very much are for example Hemmingway's "The Old Man and the Sea" or Kafka's "Metamorphosis" as well as "Tom Sawyer".

Books I thought about already are for example Nietzsche's "Thus Spoke Zarathustra" or Thoreau's "Walden". A river runs through it ? – Supposed to be great as well and I very much enjoy fly fishing, but I already watched the movie… What other books are there that come to your mind ?

I hope this post is not against the guidelines, if so, I am sincerely sorry. Thanks in advance.