For the 911 this is the seating I chose to go with (it's limited)
For the first year we have been using the Britax Companion:
They retail for over $200, but I found a new one on craigslist for $100.
It's very well built and has great inflatable airbags for head protection and support.
Without the base it fits well in the backseat, but the front seat has to be pretty far forward. When he outgrows the companion in a few months he will be in this Romer Prince:
This is the exact same design as the Porsche seat:
These are a bit hard to find, I had to order on ebay uk, the romer was cheap but shipping was a lot. The Porsche seats do show up on ebay from time to time.
I hope he won't mind the forward facing seat as it doesn't look as comfortable as the rear facing seats which allow for a lot more recline....
Both the Romer and the Porsche seat are built by Britax in Europe