The stroller that can fits in infant seat usually is quite bulky, more expensive and requires some converter/adaptor to fit the infant seat in which is not cheap either. If that is not your concern, you may go ahead with it.

Most likely you will need to buy the infant seat that can be fitted into the stroller, and getting another convertible car seat when ur baby outgrown it few months later

If your main concern is to move the carrier from the car to stroller easily then definitely a travel system would be the ideal choice for you. Yes usually strollers with travel system are slightly bigger than the umbrella strollers so most of your boot space will be occupied by the stroller.

For convertible car seats which can take newborn to around 4-6 years old (25kg to be exact), usually they can tilt a lot but not necessarily to a fully lying flat position as most carriers also do not place the child fully flat in the car.

Personally I'm using travel system from Quinny, which was a Quinny Zapp Xtra2 + MaxiCosi Cabriofix Infant carrier. I can say that this combination is the best travel system because the Zapp Xtra2 is very compact in size after folded, a real huge advantage if u are using a compact/hatchback car like MyVi.

Cabriofix infant carrier was made solid with comfortable padding. The only thing i dislike is that I can only secure it using seat belt, not with ISOFIX/LATCH because the base is sold separately and quite pricey (rm1.5k). I think the best infant carrier to use is Chicco KeyFit30 which come together with thr LATCH base for only RM1k/set.

I bought carseat when my LO already 18months old and she has exceeded the weight limit of the carrier.

If size is your main concern, Quinny Zapp Xtra2 is your best bet. It is very compact after folded, and not that heavy too.

The car seat from newborn to 18 months should be the infant carrier. Usually these cannot last so long as most of the time when the child is able to move and kick freely, they will start kicking the back seat and might even tip over the carrier.

Hybrid car seats/convertible car seats should be better as they provide more protection to the child. Most brands will ensure that the recline is enough for a newborn as long as the head does not tip forward when seating. Always remember that these seats must be able to be fitted rearward facing especially for under 1.5 years old as this is the safest position.