My 3-year-old had the original Cybex Aton as an infant bucket. At the time, it was the smallest front-to-back seat available and also one of the lighter options. It has some big annoyances though -- the canopy is a complete joke, the straps are very difficult to adjust and tighten, and the cover is hand wash/dry flat only. We'll use it again anyway if we can't find something similarly small front-to-back, but it was really annoying.
I've searched to see if there's an updated version of the guides I consulted to find a small seat when I picked the Aton (both our cars are compact hatchbacks, and now we'll need to have a car seat on both sides). I haven't found anything that's especially up to date.
Anyone have any reference recommendations that I might have missed? Or have a super small infant seat they can personally recommend?