Welcome!!
I would not recommend the Enspira either. If I am not mistaken, these were still using the old Dorel 3in1 mold for the shell before the 2012 standards changes, with the unusable top slot, short shell, etc? And they were pretty wide, actually. I am not sure what changes have been made to make these seats compliant but I am guessing they still aren't the best bang for buck in the price range. At the least, they usually make a pretty poor booster.
Honestly since your older child is FF already anyway, I would pass down the TrueFit to the younger child and install it RF, and get another seat for your oldest to FF in. How old is your older child, and what is his/her weight&height? While not incredibly narrow, you could look at getting an Evenflo Maestro (or Evenflo SecureKid400, no experience with this seat though) or if you were willing to go wider and forego the 3rd passenger look at the Graco Nautilus or the Britax Frontier (more expensive but can actually last till you can use seatbelt only, or you can pass down to youngest since it now has a 10ye expiry, IIRC).
If you want the convertible, you could look at the Radian or Complete Air, or even the Cosco Scenera, which is very inexpensive and narrow. It won't last as long as other options, but makes a very decent RF seat, leaves lots of legroom for front passengers in your model Civic (we used it for this reason), and then once it is outgrown you could pass down your TF and get a new FF seat or booster for the oldest depending on what suits at the time.