Could a native speaker help me out with this please... I've always used βολικο as convenient and ανετο/ανετα as comfortable... why is βολικο used as comfortable here?
You are right that βολικός can be translated better as convenient and άνετος as comfortable. But in Greek βολικός can take the meaning of comfortable in sentences like the above (talking about things). What would be a "convenient" bed, after all? A comfortable one. Actually, βολικός comes from the verb βολεύω which means to settle, to make comfortable/convenient, to serve well.