Swedish Plus test only review RF, as far as I know. Depending where you are (if you’re in the UK I can recommend both a group, and the makes they usually recommend) there will likely be a forum or a Facebook group or similar where you can get expert advice. There are also trained car seat experts - the challenge is identifying those people. As in the UK, I would not blanket accept advice from anyone at Halfords for example (heck, I’ve had someone at Halfords advise a seat I’m not sure even sure would have been legal for the age of the child). It varies hugely - of course some staff will be much more knowledgeable/helpful than others. My toddler (and baby) are both very big too (98th percentile plus) so I’m right there with you. As I said if you’re in UK I can send some recommendations, but regulations and seats available will vary depending where you are.