Steadi R44

I’ve not put a seat in the hold personally, but for travel I’ve got a Joie Steadi (R44 - the R129 is newer but is outside the size allowed by BA on board - my daughter has used it a few times on flights). The Joie Steadi (I wrote stages earlier - it's a Steadi I've got) is a belted seat and pretty quick and easy to fit to taxis. It fits in the bottom of a wardrobe in a hotel, and isn’t super heavy to carry through an airport if required. Also pretty cheap if it does get battered. Would buy again.

Did LHR -> SEA last year with a 3.5 year old (and back). We flew in Y. We took a car seat. I'd echo other people's comments about being worried if your child would unclip themselves in J during turbulence - I'd personally only go as far as premium eco with a toddler, but your mileage may vary. We had a lot of aggro from gate agents in SEA with our car seat as it wasn't FAA approved (it is a Joie Steadi R44 which we bought as it was the right size for BA). The flight crew were amazing and basically told the gate agents to do one. Terminal S at SEA is a hole so don't plan on spending loads of time here. Good luck with jet lag. It's a miserable experience for kids (my daughter did 8 hours last year and only last month did a 11 hour timezone shift after we went to - it was brutal).