If you're UK based, get into a large John Lewis (or similar store) and explain what the issues are and what you want from a travel system. Most JL stores with a nursery section have a 'baby john' (weighted doll) that you can borrow and push about in the prams etc. to get a better feel for it.
The whole carseat clipping on to travel systems thing: If you're planning on doing any prolongued walking with baby, it's not recommended to use a car seat for this, for baby's sake (it's advice that's meant to be given when you're being sold a system). I kinda feel the same about the prams that cushion baby a lot too, they look snuggly, but it restricts their movements and I don't like that - but I wasn't given the same advice, just a "very sensible to link the two concepts, but there is no specific advice about it". If you're just nipping out to the shops, fine, but anything over 90mins and baby should be out of the car seat for a decent (1/2h) break for a proper kick about. So, I'd say you def. need a separate carseat anyway.
I ended up opting for the iCandy Peach as I wanted the ability to adapt to have 2 children on there if needed, wanted one that went from pram to buggy, I'm 5ft3 and the handle did for me and a fairly tall DH, but the cherry looks great, is lighter (and comes in a better colour range!) I'm now awaiting delivery (of iCandy and baby) and every time I bump into a person pusing an iCandy I ask them if they have any regrets. All have said no, they're 100% happy, some even ditched others and switched to an iCandy...
It might also be worth speaking to your MW and referring for physio to support your back during pg and post-birth, if you haven't already.