I find reading books to be one of the most effective means of self-improvement. I have experienced quite a few physical and mental health issues and books were always there to help me survive. Below are some I recommend.
Physical health and longevity books:
1. Prevent and Reverse Heart Disease by Esselstyn
2. Dr. Dean Ornish's Program for Reversing Heart Disease by Ornish
3. The China Study by Campbell and Campbell
4. The Okinawa Way by Willcox and Willcox and Suzuki
5. The Blue Zones by Buettner
Books helpful for preserving mental health:
1. A Beautiful Mind by Nasar (plus the movie)
2. The Neuroscientist Who Lost Her Mind by Lipska
3. The New Rulebook by Cheers
4. Glimpses of Utopia by Scully
5. Utopia for Realists by Bregman