🚀 go-pugleaf

Palatino is a fine font for book work, and 10.5 point is an acceptable size. But I suspect that you are setting on too wide a measure, and that is making the work hard to read. Normally, a book on 8.5x11 paper should have one wide margin, with perhaps 30 to 36 picas of text width.

This will make the book longer in page count, but you can use up some of the marginal space for illustrations, headings (especially side headings), and other marginalia.

Drop into a bookstore and take a look at some of the larger format books. The are usually professionally designed and will give you good ideas.

(If you really need to cram it into a short page count, go to a two column format.)