Isofix carseat and pushchair for newborn?

You could have a look at the Quinny systems, the maxi-cosi cabrio carseat is isofix compatible & has a very good safety profile but is a bit pricy if you decide to get the whole isofix option. This carseat is compatible with a few chassis types e.g. Quinny Zap (very compact), Buzz etc.
With 2 kids we have managed to accumulate both a Zap and a Buzz - Zap is very handy for travelling & can be brought onto the flight as carry-on in the storage bag that comes with it. The only disadvantages to Zap is that it can tip easily if you hand stuff off the handles & no storage roon underneath, although you can buy some custom-made bags off Ebay or jimmi up something yourself. Buzz is much more solid & good for shopping as you can get the understorage attachment. Have a shop around & check EBAY also for prices, we got our Zap there & never had any problems with it.