Narrow high back boosters

[washngo]

Please help me find nice narrow high back booster seats for my 3 and 5 year old so they have plenty of space between seats to do up the belts! Any recommendations?

I should add, I have a 1 yo too so it is a squeeze!

Britax Adventure, narrow and without arms, so easier to do the seatbelts up.

The shape of the body (with quite protruding 'wings') on the britax makes a bit of a barrier when you have two right beside each other, so the britax didn't work too well for us (borrowed from a friend to try out).