I don't really see why book recommendations can't just be "books you enjoy".
But if you're specifically looking for "books that affect your outlook on life", you might try reading through Peanuts. It's a comic strip, but there's a lot going on in there.
Agreed. No specific book has every "changed my life", or specifically been the source of positive impacts.
But reading stories is fun, and something I do constantly. Currently I'm re-reading Brandon Sanderson's Stormlight Archive. Every year or two I re-read Dune, Lord of the Rings, The Chronicles of Amber, and Steven Brust's Taltos series. Always a pleasure.
My recommendations would probably echo those already posted, with the addition of small random stories that I remember fondly because they were just fun, interesting, or surprising (e.g. H. G. Wells: The Door in the Wall, or the original Mary Poppins books recently completed after finishing the Dresden Files for the first time.)
But if you're specifically looking for "books that affect your outlook on life", you might try reading through Peanuts. It's a comic strip, but there's a lot going on in there.