My friend and I had a brillian stay at Casa Días. The location was absolutely perfect, close to a street which runs all the way through the centre of the city.
Coffee and pastries every morning at Andrea and Luigi's cafe was a great start to the day, and very kindly included in our booking.
We were a bit worried about safety, but this apartment is in a very nice, safe part of the city and we felt very comfortable there at all times.
We would definitely recommend for anyone wanting to visit Naples.