Summer in the Balkans with a large dog - tips?

Hi there! We are an American couple living in Greece planning on leaving our island for the summer to escape the heat and are wanting to spend May-August in the Balkans. We have never been to any of the countries. We both work from home so need strong wifi and would like to go to places that are dog friendly. Near the beach is a huge plus, would like to avoid mass crowds. We also love diverse food (mainly souvlaki and Greek traditional food where we live now). Also, we are hoping for AirBnBs under ~$1800 a month for two bedrooms so cost is a consideration as well.

Which countries/cities do you think are the best given our situation?