I'm thinking about getting DD (age 2.5, about 35lbs) a new booster seat and passing the convertible down to baby #2. This would be for my husbands truck, so just for short distances around town but needs to be somewhat compact. The convertible (RF) is going to have to go in the middle seat and the new (FF) booster will have to go behind the passenger seat.

What are things to look for? Types of LATCH? Seat Belt Lock offs? Arm rests that fold up or solid sides?