Ok, i am the specialist on this.... i looked at every singly option....
1/ forget bmw seats. None fit. I physically tried them at the dealer.
2/ as far as i know, no isofix base fit if you want to have a passenger in the front at the same time.
3/ when Alice was 0-1.5 we used the maxicosy pebble rear facing and fixed it with the rear seatbelt. It worked ok. Need seat protection to avoid damaging the leather.
4/ now she has grown out of it. I went to Halfords here in the uk after looking at all porsche 911 threads on the planet. It turns out that the i8 troofline is slightly shallower than 911's.
The only seat fitting is the cheapest one they do which is front facing and only attachable via seatbelt. It is much smalled than any other seat on the market which are hugely cumbersome.
I would not use it on a dialy basis but it is perfect for occasional use. Alice is 2.
That's the one. It looks like it was designed for the i8! Stays there all the time. A bit annoying to fit with the belt at first, but once secured, it won't move!!
http://www.halfords.com/kids-zone/ca...123-child-seat