DD is currently in her stage 0 seat. We have 2 bases and can take the seat out of the car with DD in it and then move it to the other car. We are looking to get a RF seat for her to go up to. Do these still come with bases and we just switch the seat or do we need to have two seats or move one between cars? The Which reviews imply that they are really hard to fit, so would it be better to have two seats (they are expensive)? We have a focus and a mazda 6, any suggestions?