Middle seat belted or passenger seat isofix?

[NLdnparent]

Hi there
Would love some advice please.
Looking to transition to a child 4+ seat from our baby seat.
I always thought the safest positioning for a car seat was on the passenger side, but I've been reading that it's the middle.
Our car only has isofix in the two side seats.
Instinctively I assume isofix is safer than belted, but I don't know if the collision risk of a side impact outweighs that.
Is our safest option a belted seat in the middle or an isofix on the side?
Thank you to anyone who knows!
(shout out to the joie spin 360 which has served us marvellously till now...)

Middle seat advice is somewhat outdated now, and you won't get a good fit for any car seat in the middle in a lot of cars because it's often a 3/4 sized seat. A well fitted seat is more important than any other aspect of safety.

For a forward facing child, the back seat is safest and it doesn't matter which specific seat in the back.

IME it's worth getting isofix for a booster if you can, it stops the seat moving around as the child climbs into it which is annoying because invariably they push it over the seat buckle and then they can't find it but they are also in a stage where they don't want you to help them. It can also provide some lateral stability for the seat e.g. in a side impact. However, the safety aspect of isofix has mostly passed by this stage. The child is basically being restrained by the normal seatbelt, so the seat is just helping position them so that the seatbelt can protect them properly.

If your child still fits into the Joie Spin, keep them in it until outgrown. Don't move them to a booster seat just because they have turned 4 :) And if you want to, you can buy larger rear facing or forward facing harness seats even for children age 4+.