We went with a Saftey 1st convertible carseat for DS4. I'm not sure which model it is since I'm not looking at it. We did look at the Nautilus too, but the Saftey 1st seat fit him better. He is big for his age and this one was more comfortable for him and easier for us to adjust. Like the Nautilus, it is height adjustable and reclining. It too can be used as a belt positioning booster up until 100lbs. Plus, the rest arms are movable, so your child can choose whether to leave them up or down. When I said DS was big for his age, I didn't mean overweight. His weight is proportional to his height. He has always been in the 75-85 percentile for both his height and weight. I too would suggest putting your child back into a convertible car seat.