My DD is 5.5 years old, but is tall and skinny (47" tall and 40 lbs). She's been using the Evenflo Comet for the past 2 years and her shoulders are currently right at the top harness slot. She started kindergarten last August and has been asking to be switched to a BPB like the other kids. She rarely falls asleep in the car, but does on long trips or late at night, so in the Comet, her head slumps forward and looks very uncomfortable.

I noticed that Toddler Bargains 2nd ed. has the Graco TurboBooster listed as the Best Bet, but I was thinking that it may be a little dated since that ed. came out almost 2 years ago. I've looked at the Graco TurboBooster and Evenflo Big Kid Booster, which have the open loop design. My DD liked the Graco TB (probably because it had a pink flower print on it!). Are there any other seats I should be considering? Also, when should kids be using a backless booster, which I noticed most, if not all, BPB have that option?

I should also mention that I drive a 2005 Volvo XC90 that has an integrated booster in the center seat of the 2nd row. My DD has used it a few times and really liked it. Is this as safe or safer than using a BPB?

Thank you in advance for your advice!