Well, we had a good look around and have tried a couple out and think we've decided on a seat now. A Britax Kidfix; mainly due to the extra seatbelt safety features, particularly the centre guide for the lap belt as when he was in one with just a seatbelt he tried to wriggle out under the lap belt!
http://www.britax.co.uk/car-seats/kidfix-ii-xp-sict/
Will keep with the rear facing seat we have until he is a little taller (a few more cm) or gets too heavy.
Definitely want isofix, they are buried quite deep on the D2!
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Cars...
'93 Audi Coupe 2.0 Alpine White (sold)
'99 Audi S4 Merlin Purple - K04 upgrade to 412hp (sold)
'00 Audi S8 Agate Grey (Sold
)
'11 Audi Q7 4.2tdi Unknown Red (Classic Red Pearl Effect - thanks MJ)