I'd suggest basically the entire Star Wars: Republic comic series, or well if wanna get technical it's just Star Wars(1999) though at issue #49 it becomes mainly about the Clone Wars. Regardless it's a total of 83 issues and really good.
The Empire and Rebellion comic series is also good.
Dark Times series, also good.
The Obsession series
Purge series.
Darth Vader and The Ghost Prison series.
Darth Vader and The Lost Command series.
The Kotor series.
The Crimson Empire series.
Honestly there's a great deal of many good EU comics by Dark Horse to check out.
Far as novels, I'd recommend The Last Jedi series, Kenobi, Thrawn Trilogy, Darth Bane Trilogy, Coruscant Night series, The Dark Forces series, Yoda: Dark Rendezvous, Shatterpoint, Rise of Darth Vader....there's a lot frankly.
