Car seat/ harness for an escapeologist?

[Joggeroo]

DS currently in a highback booster is constantly removing the shoulder strap, then intermittantly (usually when on thedual carriageway) slipping out from under the strap across his lap. Not so bad if DP is driving and I can lean over and get him back into his seat but not good if i'm driving and there's noone else to put him back

Am reluctant to move back to a 5 pt harness carseat as am worried about the space it might take up. & just got quite confused having a look on the crelling website

Wondering what other people with similar escapees do.
TIA

Late here, and don;t know how old your child is, but my 3 stone+ 4 year old escapee is in a Britax Junior Traveller. It's taller than the Evolva 123 he was in before but doesn't really take up any more seat space.

We've got this one, but with an extra clip that goes across the chest to stop ds getting the shoulder straps off. We use it with an ordinary booster seat which takes up very little room but I have seen it used in the school taxi with a high-backed booster (didn't look as comfy though). You have to use the car's own seat belt as well as the harness.

Thanks for replying, hoped someone might be able to help. Will look into both of these options. He's 5.5yrs, how old is your LO Pixel?

We have the crelling one, with special buckles thata re harder to undo as ds3 is a talented Houdini!

Pixel- where did you get the extra strap[ fro the chest? DS could do with one but haven't seen them offered?

(Ds3 is 4.5 but small for his age)

[[http://www.mumsnet.com/Talk/1375/459623?ts=1200664595535&msgid=9294532 might help]

Joggeroo, he's 7 yo.
Peachy, the strap came included (I didn't order it the OT did) but if you scroll to the bottom of my earlier link it mentions them there. We've got the special buckle too! Even dh has trouble with it but I can do it with one hand [smug].