Switching from 5pt to booster & other questions

[lalasmama]

We've been doing multiple rounds of musical carseats lately. In a lazy mode one morning (running late), I realised that I hadn't installed the GN back in my car, so I just ran the seat belt through the booster guides, and let Lala ride in it as a booster for the mile to daycare on back streets.

The basics on her size: She's hovering just under 40 pounds--like 39.6 without shoes--and has been at that weight for almost 2 years. (We actually have an appointment with a specialist about this, so we're hoping she will get to the other side of 40 soon!)... She's about 44 inches. She turns 6 in 2 weeks.

So, a few questions:

(1) Do I just take the harness straps out to use it the GN in booster mode? I can't find the manual as we recently moved.

(2a) At 6 years old, is there any reason to keep her harnessed if she's sitting and behaving in the GN as a booster? The belt goes right between her shoulder and neck, and low over her hips. (2b) We have a Marathon that she still fits in--her shoulders are still 1/2 inch under the harness slots without the cover on. Its still fine for her to be harnessed in this since she's still within the size guidelines, right? Is it any better/worse for her to be boostered or harnessed? The MA has been a back-up seat for whoever needs it, and I'm thinking about selling it and putting that money towards a back-up booster.

(3) SO is begging to let her use just a backless booster in his car (the same Cosco no-back one that he bought for his 6 year old, 55 pound nephew). It has lap/shoulder belts in the center, which is where she would sit. How safe/unsafe is this to do, assuming she's hit that 40 pounds? Am I correct that a high back booster is safer than a no-back booster?

Thanks for reading this and any advise. I'm soooooo confused about all this now that she's a "big kid" and not my tiny little toddler now!

[o_mom]

(1) I'm not sure if there is more to the conversion, but the manual should be at www.gracobaby.com (http://www.gracobaby.com) go to 'Help Center', 'Product Instructions' to find it.

(2a/b) If she is a half inch from the top slots of the MA, she may have only 6 months or so left. I normally like to see kids over 40 lbs before moving to a booster, but at 6, I would be OK with it. My own 6 yo is a similar weight, but shorter, and uses a booster occasionally. There really isn't any data for older kids to say if harness or booster is better (5 and under have a higher risk of head injury, though). You could keep the GN harnessed in the main car and move to a booster in other cars as another option.

(3) A highback booster reduces the risk of serious injury or death by 70% vs a backless, so it is best to use a highback as long as possible. Additionally, with a smaller kid, it is better to keep them in a highback longer to let them develop wider shoulders and a heavier base to keep the shoulderbelt positioned better. The other thing to look at is if his center back seat has a headrest. If not, she will need to use a highback there anyway.