A couple other comments-
First, if you have inflatable seatbelts, there are restrictions for using with some car seats. Please double check your manual.
Second, the middle may or may not be significantly safer than an outboard seat. Existing studies on children in appropriate restraint systems are quite old. They do not generally include vehicles within the last 10+ years that have widespread adoption of side curtain airbags and stability control. In addition, crash safety testing has advanced considerably since 2011 or so, and newer vehicles perform much better than those from even 15-20 years ago.
Car seats have also improved, especially in the area of side impacts, and rear-facing car seats tend to be even more protective in side impacts. If we had a recent study, I would not be surprised to learn that there is not a statistically significant difference in severe or fatal injuries for a rear-facing child in the center vs. outboard seat of a vehicle from the last decade or so. Even less difference in a larger, taller vehicle like an SUV, truck or minivan.