I have a newborn and a 23 month old. I use a sling and our usual pram, or sling and ds goes in a trolley while we grocery shop, or I make DS walk and hold hands (I tought him to hold hands before bubs came along) if we are just ducking in somewhere or doing something with/for DS. So far I haven't gone "oh I wish these two were both in a pram!". Maybe you could try this out before getting a pram? That way you may decide you don't even need one, or you can get one that is exactly suited to your needs before jumping in

The beauty I've found with having bub in the sling (I have a hugabub) is that she sleeps in it as soon as she's popped in (she must feel all snug n'stuff) so I'm really only dealing with the terrible toddler and not toddler and screaming newborn.