Car seat help

We are going on a 11 hour road trip and we have a 2 year old and a 2 month old so at some point I will have to get in the back seat and feed the baby in his seat. How ever in is car there is no room in the middle at all I can hardly fit and I’m super tiny. So we decided to take his truck (I call it a half back seat cuz it’s not big) so I decided maybe we Can get upgrade his car seat and get him a booster seat with a harness i found two I’m looking at. We need space both in seats and where his legs go. (The Greco one he has at his mom and it looks kinda slim) please help pick one