We have this, you can't attach a car seat but as the above poster said, we've used the newborn cocoon since birth, now he's 3 months we're are putting him flat in the normal buggy chair.
What is your budget? I went with the mountain buggy nano duo, it's very compact and fits through my front door and on the bus. Folded up it fits in the boot of a Hyundai i10. it's a double stroller that you can attach a newborn cocoon and a car seat to. Only thing is you have to buy the car seat straps, rain cover and cocoon separately and does cost a fair bit. However you could find one second hand x
I have the Venus double. I’ve not tried to attach a car seat to it but I love the pram. It’s so handy for us, I have a 2 year old and a 6 month old and have been using it for the past 3 months. It lies flat for newborn or you can get a bassinet to for the seat. As it laid flat I never even thought of attaching the car seat to it. The fact both seats operate independently is great and my toddler loves sitting next to his sister. The only thing I’d recommend is getting your own footmuffs for it as the branded ones that come with it are rubbish. X