Slim carseats

[singlewiththree]

I've just got a Kia Sedona and am wondering what carseats best fit in the boot?

I have a 3yr old, 4 yr old and a 4yr old to sit in the boot.
2yr old and a 16mth old to sit in isofix seats in the back
9yr old (mine) in the front.

I'm struggling to fit 3 high backed boosters in the boot seats, I can manage two high back and 1 with nothing but my 9yr old complains being in the boot.

Can you recommend any solutions?

[FizzysFriends]

Are the 4yr olds tall enough to go on a booster without the back?

[singlewiththree]

I think so but I can't seem to fit 3 boosters in the back.

[FizzysFriends]

This is what I use and they are much narrower than any other I tried

http://direct.tesco.com/q/R.206-4508.aspx