We went to Croatia - Dubrovnik - for the first time last June and both really loved it. It is very scenic and clean, though not, I think, an area with many beaches. Mostly people swim from platforms on the rocks - but the sea is very clean and clear. There are several short (and longer) boat trips you can do from Dubrovnik - e.g. to Cavtat (30 mins by boat) and Lokrum (10 mins by boat), both of which are peaceful and lovely. Two sisters in my choir had a holiday in Cavtat last year and they thoroughly enjoyed it.
My neighbours go to Split every year, which is also supposed to be very nice.