http://ball-pythons.net/forums/showt...t-Thermometers
This thread has some great info, just about everything you need to know as far as heating is concerned. Also, I strongly recommend buying direct from a reputable breeder. They are usually very helpful, and are out to make you and your snake happy, not make a quick buck. A few great places that I reccomend are Brian at BHB, Garrick at Royal Constrictor Designs, Dan Wolfe, Ozzyboids, Jon at Cold Blooded Addiction, Justin Kobylka, and Mark Petros. There are a ton of great breeders that could hook you up with a fantastic snake, as well as help you and it thrive. Also, these people may not list normals on their site, but they may have some unlisted, and would be happy to give you one for a nice price. Best if luck, and they are REALLY addicting!
Edit: whoops, missed the fact that you are in Greece. Might be a little harder to come by a BP there.