We travelled to Bulgaria with 2 children for 14 nights.
The flights were with Wizz Air (low cost) from Luton. I have used them many times and they have always been great.
We stayed at the Selena Hotel in Sozopol which is opposite a lovely beach and the promenade. The hotel was amazing and all the staff were so helpful.
Bulgaria is getting more commercialised, however Sozopol is still very Bulgarian.
There is no need to go any more than B&B because it is so cheap and the selection of restaurants is immense. A bottle of white wine in the local shop is 80p!!!!
There are resorts such as Duni close by so you can visit the beaches or shops there. A little road train runs every half an hour to and from Sozopol to Duni.
A great country to visit to avoid Euro prices!!