Having just gotten rid of my Celica for the is300h, because of a new baby and a long legged 7 year old, I highly recommend the jolie360 spin, its isofix and is rear facing/ front facing from new born - although we waited until bubba was 7 months as the clip in car seat/ pram adapters are bloody useful!
Isofix was a dream and I like the fact there is a top anchor point on the Lexus (my husbands older isofix corolla doesn't have this).