That's really great that you heard the heartbeat! I'm sure monday's scan will be fine and you'll see your little baby bouncing around in there.
We have a travel system, so we use the car seat from that at the moment, but I don't think it's very comfy. We've only left him in it and clipped it onto the stroller twice when he happened to be sleeping cos generally he's not very happy in it. Usually we take him out and put him in the pram/stroller. Our particular pram/stroller converts into a pram / carry cot shape so the baby can lie flat. I was going to post a link but it seems they don't make it anymore
We used that a lot when logan was small. He even slept in it for the first 2 or 3 weeks i think it was.
When he was about 14 weeks i think (i forget exactly) we converted it to the stroller (he was able to hold his head very stable at that point). He was getting too long for the pram setting. Now he sits in the stroller and looks around. You can adjust the backrest to 3 different settings, so either sitting up very straight, or slightly inclined (wihch is what we usually use at the moment), or lying down so they can nap.
And our travel system folds with the umbrella fold so fairly compact and fits in the boot of my tiny hyundai atos!
My brother and sil bought a monster of a travel system and landed up having to by a bigger car so it could fit in that!
We borrowed my friend's stroller on the weekend (her daughter is 2), and i must say that is super compact and really light and was nice in that regard, but i don't really see us getting one like that because although it's super easy and convenient to transport/carry, it felt a bit too 'dinky' for me. It's quite short (i'm fairly tall - 1.72m) and just felt a bit like a child's toy. i like that our travel system stroller is quite sturdy.