Two suggestions:
Westerns: the old Hopalong Cassidy stories by Clarence Mulford, hard to find but good. Also very different from the character portrayed by William Boyd on TV and in the movies. But that's OK, gives us two different story sets.
Spy: John LeCarre (pseudonym), a guy who had been there, done that in British intelligence. Not your usual technology focused spy stories, but focused on the people and the relationships and the psychology of spying. His books, like Spy Who Came in from the Cold, Tinker Tailor Soldier Spy, Russia House, Tailor of Panama, etc., are very deep, very thick, and not always positive. After reading The Honourable Schoolboy, I was in a massively foul mood for 3-4 weeks. They are that good. Here's a hint - read 50-100 pages, then start over, much easier to get his pacing and style that way.
LeCarre is the best author IMHO short of Shakespeare.