IMO Toddler seats are useless if you toddler still naps. They don't recline, there's no shade and they don't look particularly comfortable (or safe IMO, since they change the weight distribution). I've also hard they aren't easy to push. If its just for the shops and quick trips a toddler seat is probably fine but if you walk a lot, or are out lots or around nap times and want him to sleep then I'd get a double.