DC3 due in 2 weeks. Several months ago we visited a specialist car seat company for advice on how to safely fit 3 children into our car in car seats. They gave us a selection of options, with a strong preference for one option, which they said was the safest. The option is that we have 2yo in ERF seat in the middle, then nearly 7yo in group 2/3 seat on one side and infant seat on the other. This apparently fits the best too (nb they tried out all other 3 in a row combinations and it doesn't work any other way). We have tried it out this week and putting 2yo into the middle has done DHs back in. DH is the one who predominantly puts them in and out. DH historically has back problems and has physio for it - the physiotherapist wants him to limit the things that make his back hurt (especially as he has a manual job), so we really can't use this current formation.
Other options from specialist company (although they didn't specify which option was the best). Option 1) Put nearly 7yo into backless booster (which is narrower) in the middle of the row - she is over the minimum weight and height limit for a backless booster. My reservation with this is lack of head support. Option 2) Put nearly 7yo into the boot in stage 2/3 seat, where we have another row of seats. Reservation with this is that if we had an accident she would not be able to open a window and climb out (although DH has questioned if we would actually want her to) and also don't think we could fit much else into the boot (which we do currently utilise quite extensively and so wouldn't be able to use this option for longer trips, e.g. when we have buggy and luggage).
My current thinking is that we get a backless booster and use both options depending on the scenario, but DH says it's a faff to keep moving seats in and out (it is and involves having to move the back row and take the ERF seat out each type - takes about 15/20 mins and isn't great for his back).
For context all children use the car 2-3 times a week. We probably average 2 short local journeys a week and 1 medium trip (20-30 mins each way) once a week, trips over an hour are once bi monthly and then over 3 hours once a year.
It would just be really useful to have other peoples thoughts on what they would do in this situation. We're really struggling to decide on the safest and most workable option for us.