I really recommend the Complete Chronicles of Conan by Robert E. Howard. Everything you need, including unfinished stories (without any later author’s attempts to “finish” them, collected in one book.
Just like in the real world, different Hyborian Age cultures developed technology at different paces. So we have people with full plate armor fighting people with copper or stone weapons. At least no culture in the Hyborian Age has developed gunpowder.