I'm a big fan of backgrounds and so I'm very biased towards them, but...I would actually encourage you to come up with specific designs for your characters' homes if a lot of the conversations take place there. They don't have to be really complicated, but you can show a lot about a character's personality through their living space. Are they messy or tidy? What sorts of trinkets do they have around? Is their furniture plain and practical or ornamental? What colours do they like? When they're more limited in how much they can customise their living space (military barracks, school dorms, hospital room, prison cell etc.), you can also use it to help establish your setting.
As for avoiding floating heads, I vary the angle and distance of the camera. Close-ups are good if you want to highlight facial expressions, and coming further out can show other body language (hand gestures, set of their shoulders, if they're fidgeting, playing with an object etc.) and help keep the conversation grounded within its setting. When I indulge in short sequences of exposition, I sometimes draw what they're talking about if I think it provides something informative and interesting for the readers to look at.