Here are some car seats that allow harnessing to 25kg/55lbs
Britax 2 Way Elite Rear or Forward facing 9-25kg.
Britax Nordic Secura Rear facing 9-25kg only.
Britax Nordic Multi Tech This can be used 9-25kg rear facing, 9-18kg forward facing and 15-25kg in High back booster mode.
Brio Zento Same set-up as Britax Nordic Multi tech.
I have the top 2 seats (2WE & NS) for my DD1 3y/o 16kg 101cm tall and my DD2 20m/o 11kg 85cm tall. Both are rear facing and they will stay rear facing until they out grow the seats. I have seen the side by side crash test videos of rear vs forward (i.e. both seats on the same test sled) and just couldn't do it on a permanant basis (forward face).
DD2 has never forward faced and DD1 has only forward faced about 10 times since she hit 13kg (spare seat is Britax First Class so no rear facing over 13kg). DD1 has only been sick once in the car but as she was sick the rest of the weekend I don't think it was travel sickness. DD2 has never been car sick. They do not fuss about being rear facing even though DD1 has experience of foward facing and she enjoys rear facing more.
They do take up space BUT my 6'2" DH has room to sit comfortably in the driver seat (though it is further forward than it used to be) my seat is even further forward than DH's because the Nordic takes up more space as it has a recline function. I am still comfortable and I am 5'8".