Booster seats

[ThingOne]

My very small 5.6 year old is growing out of his 18 month-4 year old seat (finally) and I need a booster seat for him. He's not very tall, possibly 105cm and weighs, probably, around 16kg.

What do you recommend? I'm a bit worried he'll get all grumpy when he can't see out of the window, sob.

depending on your car he should still be able to see out,
do you have isofix?

Thanks all.

We're having problems strapping him in, and he's complaining that the strap squishes his willy.

And no, he doesn't seem to mind at all that he's in a "baby" seat and all his friends are in boosters.