So I am looking for something pretty specific. My DD is almost 4 1/2, but she doesn't quite weigh 30 lbs yet. I am not ready to pull her out of her car seat, but I am looking to get a high back booster/convertible seat combo to have on hand. I have looked at some, but honestly don't really know much about them. It would be used when she goes with MIL, my sister, my cousin, etc, and if we bring friends home from school for play dates. We would be using the harness for a while when we do use it. I just don't want to buy another regular seat as we will eventually be moving DD to a booster. Although she might be 7 before we get there weight-wise! lol The one key thing we need though, is something that is pretty narrow. It would have to fit between DD's Graco MyRide and DS's Britax Marathon that is still rear facing - does this exist?? TIA!