best compact car seats

Has anyone had any luck finding an infant car seat or convertible/5harness that is super slim to fit 3 in a row.  I drive a 2016 Chevy Trax (smaller than the Traverse but bigger than a Cruze if you know Chevy cars) 
I have two kids already and they are in 5 harness seats.  I'm no where near ready to put them in just a booster even tho they are big enough. Ages 4 and 5- and both around 50 lbs I want them safe as can be. 
Which car seat brand fits 3 in a row? 🤞 we are hoping to keep my car when we have a baby.