"OK Bulgaria" is the name of the agency? The Notary Act has to be in Bulgarian, usually with an English translation for Brits, but the Bulgarian one is what counts - if there's a difference then what's in the BG version takes precedence.
Are you going to sign in person or have you given POA to someone?
I don't live in that area, so can't really help regarding a local lawyer, I'm afraid; ideally your lawyer will also attend the signing of the Notary Act to ensure there are no last-minute "glitches".
It's better if you are there in person - that way you can check that the house is in the condition it was when you last saw it...