We used a Jane Matrix car seat and travel system in our IS200
The matrix is a clever thing that is like a carrycot for the first few months (which is apparently better for the baby) and is fitted across the back seats, then it tilts up to become a rear facing seat.
We got it as part fo a travel system, so the car seat attaches to the buggy so it looks like an old fashioned pram, or it can be tilted up. There are various different buggies available with 3 or 4 wheels. Ours takes up quite a lot of room in the boot, but is ok day to day: you can get the buggy, all the other day to day junk and a weeks shopping in. I bought a roofbox for longer trips away: seemed a lot better compromise than buying a lumbering estate with a boot that would only be full a couple of times a year.
Now we have got a foward facing seat for our 2yr old we just use the buggy on its own.
It's a bit fiddly to fit , and takes up the whole back seats in flat mode, but worked fine in our IS.
Have a look here:
http://www.jane.es/seguretat/fitxa/matrix/index.php
if you are after a travel cot, we got a Graco Compact one, mainly because, when folded, it fits in the boot in the space between the wheelarches , leaving room in front for your Jane pushchair!