I found listening to the audiobook version of Viktor Frankel's 'Man's search for meaning' was very helpful. Funnily enough, I have read the book but got more out of the audiobook.

I know you don't want to hear more fitness, but weightlifting made a huge impact on my outlook. Try 'Starting Strength'. Getting strong makes all the little aches and pains go away and you hit new, easily-measured goals.

Finally, visiting the deathbeds of family made me realize that the only thing you carry at the end of your life is the love that you've fostered. Seeing the world through that lens truly changed me.