I recommend Manuel's Airbnb. It's situated over six kilometres from Piazza Maggiore and about three from Bologna airport. It's well-connected to both the city centre and airport, and is located in a safe and quiet neighbourhood. There are two large supermarkets nearby. And the kitchen is well-equipped. Manuel gave my girlfriend and me homemade cake on arrival.
However, the breakfast wasn't adequate. And the WiFi kept going off from time to time.