Why visit paltry little Slovenia when Croatia is right next door?
I would argue that Croatia has everything Slovenia does, but more. From ancient city cores of Pula, Zadar, Split and Dubrovnik, to national parks like Plitvice Lakes or Krka. Also, and I think this is pretty obvious, the beaches and the entire Dalmatian coast (especially islands - Brac, Hvar and Korcula) have some of the most stunning scenery imaginable and, as advertised by Alfred Hitchcock, the most beautiful sunsets anywhere in the world.
As far as crime and safety are concerned, there's nothing for you to worry about in that regard. I've never felt unsafe whilst there and I legitimately enjoyed my time there. People are very hospitable, the days are long, relaxed and there's always the opportunity to fill them with all sorts of activities - from swimming, hiking, kayaking, boat trips and clubs and bars in the evenings. You'll never be bored in Croatia, I promise you that.