ERF for large baby/toddler?

[Fruu]

My boy is 15 month old and rather tall / heavy for his age (75th percentile or a bit above?) We need a second car seat for the GP's car - a newish Landrover Discovery Sport which has isofix points.

We got the BeSafe iZi Plus for our car because we don't have isofix points and it's good ERF up to 25kg / 5 years.

Does anyone know whether the isize regulations or the Swedish plus test is better, or have any seat suggestions? I want my boy rearfacing for as long as possible but I'm not sure whether to go for an isofix / isize seat which he may grow out of rather quickly but will be easier to fit, or whether to go for a belted seat that will last longer rearfacing.

To go for fittings, we're close to www.pramworld.co.uk, I might be able to persuade the GPs to go to www.securatot.co.uk although baby and I will be unable to come along, and we have all the normal high street retailers, John Lewis etc near me.

Thanks! :)

Swedish Plus tested is better than i-Size, it's the strictest test there is and measures neck loads (which no other test does).

You need another seatbelt-fitted seat really, the trouble with going for an ISOFIX seat is what do you do when your son outgrows it? You'll have the choice of a high backed booster (not safe for a child under 4, and preferably shouldn't be used until a child is 4 1/2 due to their skeletal development. It doesn't matter what they weigh) or buying a 25kgs rear facing seat, which you could have just bought in the first place!

There are 3 seats on the market which have harnesses that can be used up to 25kgs forward facing, which you could also consider for your son when he outgrew an ISOFIX rear facing seat, but they are all over £200. It would make more sense to buy a 25kgs seat now and then go straight to a high backed booster aged 5. You can get a decent safe high backed booster for £50-£70.