I find this incredibly strange. He specifically asks for books that “do not break a person’s spirit” and you recommend possibly the most well-known nihilist?
Samr, if you’re still around and still reading, Rothbard’s Ethics of Liberty is standard around here, however it’s a bit more advanced, and most would recommend getting through For a New Liberty first. (See the links section at each of those pages for a download of the full text in different formats…including audiobook)
There’s a 10 lecture course by Roderick Long titled “Foundations of Libertarian Ethics”. In fact, check out all the media from a search on “ethics”.
Herbert Spencer authored Principles of Ethics volume 1, volume 2. (You might also check a search in the literature section as well)
And finally, Walter Block as written extensively in the area you’re kind of asking about…see here.