Best booster for older child

I am in need of a booster for my 9 1/2 year old, right now she's currently in a backless booster but I need a high back booster that can also be used by my 7yr old niece from time to time.

My daughter is 52" tall and about 59lbs and 9 1/2 years old, she's a little short for her age and I'm just not comfortable with her being in just a seat belt yet.

My niece is almost 7yrs old and about 45lbs and about 47" tall.

I have a 7 passenger 2005 Pontiac Montana and during the summer I'll be keeping my sisters 2 kids as well as my 4. I need a HBB that will accomodate my daughter when she's riding in it and my niece when she needs that seat.

I was looking at the Monterey because I liked that it went to 120lbs but didn't know if there was anything else out there that might work for us?

FWIW, this will be in the 3rd row of the van with a Radian 65 and a Radian 80 so I need something that's going to fit!

Thanks!

I have no personal experience with your van, so I have no idea what will fit in the third row with two Radians. I do have a super-tall 7yo (53.5 inches) and have used many highback boosters, so hopefully I can throw out some good options. I can tell you, though, that you're right that your dd will need a booster for awhile longer, probably 2-3 years. Age and weight don't matter as much as height, and even then, there's no real set height limit when it's okay to forgo the booster; it all depends on the vehicle seatbelt configuration, and how it fits the child. A child can fit fine without a booster in one vehicle, but still need a booster in others.

Boosters I'd consider, that should be tall enough to work for your 9yo for a few more years, are the Sunshine Kids Monterey, the Recaro Vivo, the Graco TurboBooster and the Graco AirBooster. The Monterey and Vivo are taller than the others. The Turbo tends to fit best (of those four) in tight spots. There aren't a ton of great booster options on the market right now, in my opinion, especially not boosters that fit great in three-across situations. If none of those four work three-across, I'd try to find a Fisher Price Safe Voyage booster (online). These were made by Britax for a short time, and have a width-adjustable base, and armrests that sit pretty far forward, and no real torso wings to speak of, which makes buckling easier than other boosters next to another carseat. The FPSVB is pretty short as a highback, though; my daughter is now too tall for highback mode, unfortunately.

My long-legged 7YO likes her Air Booster, and they're on sale at Big Lots for $55. This thread shows that the shape of the back of the booster allows a bit more room for buckling: http://www.car-seat.org/showthread.php?p=782745

Does your van have top tether anchors in the third row? If so, another possibility would be the RideSafer Travel Vest www.ridesafer.net

Thank you! I'm going to head to Big Lots today and see if they have the Air Booster still for sale.
I love the look of the Monterey and that it would last us longer but I don't think I'd be able to if it 3 across with 2 other radians because the shoulders adjust to wide.
I also like that the Air Booster has the better leg support