Need new car seat!

alake

We moved to southern Florida from Canada this year in September.  We have 2 little girls. We are flying home to Canada for Christmas, and I don't want to take there large seats on the plane.  Here are their stats

S. will be six on Christmas Eve.  She weighs 45-47 pounds, I will weigh her tonight.  She stands 43 inches tall, and has a 14 inch torso.  She is booster trained, but still rides in a harnessed car seat.  

L is 4 years and four months.  She weighs 34 pounds, stands 37 inches tall, and has a 13 inch torso.  She is still harnessed full time.  

They currently ride in Prosport harness car seats in my truck, and Frontier 85s in my DH's truck.  We fly quite often with them.  Before we made the move down here, we flew almost every other weekend from May through to September due to my DH's work.  We used a booster seat, Graco high back booster for S, and a evenflo Maestro for L.  We left these in Canada when we moved, as a friend of mine had her small 2 year old in a graco no back booster, and her 5 year old completely out of a seat.  I wouldn't mind getting another Maestro for L, but just wondering if there is any better options.  We won't be flying as often, as my DHs job is stable, and in one location.  These will just be used during school holidays when we can make it home.  Also what kind of booster for S.

Any opinions would be great.  Sorry this is long.