Help! We need a bigger car seat now that Sophia is bigger, but...! We don't have a car, but need one for when we see Grandparents. Obviously we can't carry one down with us when we go see them, so they'd need to keep one down there, and they wouldn't need it in the car all the time. How do the bigger ones work? Do they all have to be bolted in, or do some strap in like the smaller ones? I saw some on argos but it doesn't say how they attach. Any help much appreciated!