any advise on graco high backed boosters

[sazm]

hi all.
atm we have 2 britax hi-liner/adventure seats for our 5yo(115cm) and 7yo(120cm), and a britax eclipse in the middle for our 2.5yo.
the hi-liners have their headrests up to the correct height for our 5yo,but our 7yo is needing his to go higher,the problem is that the headrest cant go any higher as its actually jammed between the side of the car and the eclipse in the middle.
i had a look in halfords at the 'rally sport trilogic' graco seat,it seems pretty well padded,and the headrest is not nearly as big as the britax.
our options are - put our (just turned)7 yo in the middle on a basic booster and keep the eclipse and one hi-liner.
or
put the eclipse at one side and hope that the 2 graco high backed boosters for the older 2 will fit in the middle and at the other side.

our kids spend lots of time in the car and also sleep in the car a lot. thats why we originally bought the britax sue to the shape of the head rests.

any opinions welcome :)

they dont fit in with the eclipse at one side,because of the way the seat is shaped it means we loose about 3 inches from the width of the back seat.

i know my sister had a graco a few yrs ago and it was awful,no head support,juist wondered if the newer models were actually better safety wise or just looked nicer/had more padding.
problem is,theres no shops around me which you can try the seats out in!even mothercare etc in 100mile radius are all in the middle of shopping centres!