Can anyone help please? We have an (old) Mercedes estate and we are just about to have our third child. I have my 5 and 3 year old girls on booster seats and have just bought a baby car seat (the bucket ones). But they won't all fit in the back seat! Before we go and spend money we haven't got on a 7-seater, does anyone know of any narrower booster seats or have any advice / help to share?! Thanks