I am assuming that is your first child. First, congratulations!.
I have a 3 year old and an 9 month old boys. Here is what I found: with my wife's old 2000 honda civic: with an rear infant carrier and snap on base getting in an out you have to literally do that while looking at the roof to save your back (I am 5'10"). Also I have to tilt it a bit to clear the carrier' handle from the top of the door opening. If you don't have a snap on base might just slide it out. (With a snap on base is more secure and you don't have to deal with the seat belt every time)
With my Mazda 3 hatchback, I don't have to do tilt the carrier that because of the extra height. With my wife's new CX5, is a bit challenge for her to unload or load the carrier because of the extra ride height (granted she is just shy of 5'). For me no problem, at least I don't have to stare the roof while doing that. Granted I have to make sure that I have enough side room to open the door. So a Mazda 5 with sliding door are good feature. As a added benefit, the CX5 has more rear leg room that my 3 year old can't kick (for now) back of the driver's seat.
So here is what I suggest: eat more spinach so your arms can be like Popeye

j/k you will find out soon.... kidding aside... get your baby carrier and ask the dealer to try it out in each car to see what works best. They will gladly help you to narrow your decision (off course they want to sell you a car). To be more realistic, get a bag of rice, beans, etc... to simulate the weight of the baby. I recommend 20- 25 lbs for worst case scenario. yep. I can't wait for to switch the infant carrier to a regular front facing child seat for my 9 month old son.
As for trunk space, granted the CX5 has more than the 6 (34 vs 14 cu ft). However, on the CX5 it measured from the floor to the roof line. If you measure up to the cargo cover or where the top of the back seat cushion, I think is about the same or a bit more like 23 cu ft.
Anyway, I hope this helps