carseat hell

Today we went to wally world to try and get a convertible carseat for Evan. I really liked the one we had gotten last week which was the Graco myride 65 but it just wouldnt fit in our car :( we have a compact car the chevy cobalt which makes getting a carseat in it a pain. Evan weighs 16 lbs so we have about 5 lbs to go before we really have to look into getting him into a proper fitting seat. I think that will be at the 6 month mark so we have a little over a month to research this topic. I need one that fits and will keep my guy safe if we were in an accident. I have been recommended the Scearna and then get the Nautilis when the time comes for a bigger seat. I am leaning towards that idea since the person recommending it, I trust her opinion highly. Any additional suggestions on this idea would most definitly be appreciated!!