When I'm at home, usually I purchase pizza from Pizza XL, the websites from where you can do it are www.amam.bg or www.gladen.bg I'm not sure which one has an English menu though. The dough is quite thick and the ingredience are not always matching the amount of dough, but try them and then give feedback. Just make sure not to try the pizza with Frankfurt sausage - it's the worst pizza I have ever eaten or at least is in top 3. Good luck with your pizza hunting and let us know which pizza have you found as the most delicious in town!

P.S. Have you tryed Bulgarian pancakes? If you haven't, make sure to correct this mistake. The best pancakes (not exactly pancakes, but bigger and called Катми) in town can be found at Borovo Market. Just take the 9 trolley and get off at the last stop, then go towards the avenue where the other trolleys and bus 204 stop and just 50 meters past the stop on the right you'll see the stand with the pancakes, they have various topping you can choose from, I usually take one or two with chocolate and one with ham and Кашкавал cheese.