Hi,
Agree with Peter, the time of the year you have booked is going to be very hot and laying out in the sun for more than an hour COULD be out of the question.
I have been to Bulgaria 3 times (1999 & twice last year) and i have seen everything that Sunny Beach has to offer.
As i was only about 13 first time i went, i didn't have much of a complaint about much stuff at all.
The beach is about 6km long and you can walk the length of it on a walk path with shops and bars all the way down.
I find the people there very nice and we made friends with a couple of people which is the reason we returned there for a second time in the one year.
I will be making a return regardless of if they're in the EU or not, as i love most things about the place.
I would STRONGLY RECOMMEND that you only go B&B and eat out resturants as the hotel food can be very poor.
Any questions, please just ask.