The best advice I can give is to visit Bulgaria and spend a few weeks seeing the country. Many expats opt for village life but find the reality very different to their expections. In rural areas services are generally very limited, with many villages having few shops, bars or restaurants. Although people in the Bulgarian countryside are usually very friendly and welcoming, few will speak English. Be prepared for a sense of isolation, particularly in winter when some communities are cut-off regularly by snow. You may also need to consider access to medical care or good schools if you have children.
Saying all that it is a great country to live in. It's cheap, hot and laid back. Do your reseach on the internet and employ a lawyer when you buy a property.
One other suggestion. Why not rent for 12 months before buying ? That way if you don't like it you have not burnt your bridges. You can pack your bags and return to the UK.
Good luck.
Best,
Paul