Start with high-confidence sharpening your memory books, then narrow by subgenre or adjacent topics.
The Invincible Brain
Majid Fotuhi
The Memory Bible
Gary Small MD, Gigi Vorgan
Remember
Lisa Genova
Fluent Forever
Gabriel Wyner
Make It Stick
Peter C. Brown, Henry L. Roediger
Change Your Brain, Change Your Life
Daniel G. Amen M.D., Daniel G. Amen
Keep Your Wits About You
Vonetta M. Dotson PhD, Vonetta M. Dotson
High-octane Brain
Michelle Braun, Karen Postal
Change Your Brain Every Day
Daniel G. Amen, MD, Daniel G. Amen
You Can Fix Your Brain
Tom O'Bryan, Mark Hyman - introduction
The Age-proof Brain
Marc Milstein
Functional Training for the Mind
Jeremy Bhandari