I found a book that meets even my strict criteria - it is written by a trusted person, Glen Copeland, who works in both the U.S. and north of the border in Canada. Not only does he deal with foot problems for ordinary folk, but the ingrown toenails of sport teams (like the Toronto Blue Jays) have benefited from his knowledge and experience.
It has plain, yet factual information on the problem of ingrown toe nails and has a whole range of treatments and cures.
So, give it a look see. You can preview a number of pages of the book. Check out The Good Foot Book