Car seat for tall, heavy 3 year old

[EveMoneypenny]

DS has just turned 3 and is very tall and solid (about 104cm, 17.7kg). He has been rear-facing until now in a Maxi-Cosi 2way Pearl, but he has definitely outgrown it now and I am going mad trying to make sense of all the different options for our next seat.

Basically, what I would really like doesn't seem to exist, and I think my choices are between

1. A forward-facing high-backed booster or group 1, 2, 3 combination seat. I think I would be OK with turning him forward-facing at this stage, but I would be concerned about not being able to use a 5 point harness or impact shield as these only seem to be suitable until 18kg. I would be concerned about him wriggling or falling asleep using the car seat belt. Are there any seats that harness beyond 18kg? I think the Diono Radian 5 does, but then Which scored it 20%! Or are there any hbbs that are better at having a child securely in position with limited wiggle room?
   
   
2. Erf to 25kg seats. However, we are in Scotland, so can't exactly make a trip to Milton Keynes to check these out in person, and the lack of isofix is a bit of a disadvantage. I guess the Britax TWE is the obvious choice here, though.
   
   I'd be very grateful for any advice!

[SleepFreeZone]

Britax two way elite

[SleepFreeZone]

I have my four year old in it front facing and it's great. Once he is 25kg he'll then move into a high backed booster and we'll keep it back for my one year old once he outgrows his current rear facing seat.

[EveMoneypenny]

That's definitely a contender, but for seats bought after May 2017 it can only be used ff with harness until 18kg (rf until 25kg though) which puts me off a bit.

[Spanneroo]

Radian 5 and TWE are the only 25kg harnesses I'm aware of.

If it helps, our DD has just turned 3, is 114cm and 20.5kg and she's still very comfortable in the TWE and I'm not worried about her outgrowing it before her 4th birthday, which is when I'd be happy putting her in a HBB. In fact, I'm almost certain she's not even on the highest harness setting yet.

Have you contacted the ICSC to ask what they'd recommend for your car and child? They may also have some insight into why the newer models say 18kg FF (possible it's just legislation that came in with isize rather than safety IYSWIM)

[stackedcups]

Axkid Minikid for RF or Joie Bold or Cosy n Safe Excalibur for harnessed booster

[stackedcups]

Sorry for brevity, feeding baby

[Helspopje]

At age 3 taller but fractionally lighter mine all went in rodifix.
Didn't work about wriggle room as all were able to be told not to fiddle with the seat belt and complied

[Helspopje]

Worry not work

[EveMoneypenny]

Thanks for all replies!

Cozy n Safe Excalibur looks great judging by reviews, but can't find any info on its safety testing eg Which? Also doesn't seem to be stocked by any shops locally. Still, it's £125 at Asda just now which is a bargain...

@spanneroo, I think it's because they had to change the buckle design.

[Kimber2]

The britax marathon reclines and has a five point harness to 65 lbs, but at age four our daughter went to the britax frontier 85, they have European safety standards, a 5 point to 85 lbs, booster to 100lbs.
You can check on buying online from incarsafetycentre.co.uk