How old is your grandchild? If a few months old, and not a newborn, it may be more cost effective to purchase one of the small, lightweight, compact strollers, something like the Graco Travelite Stroller (which is actually, suitable from birth to 3 years), and folds like an umbrella. There's loads to choose from on the market, and most will fit in the footwell of a car, so you'd have the whole boot space for the dog. When I had my kids, we had a lovely pushchair, but I ended up buying one of those Maclaren umbrella strollers, and used it all the time! Obviously, you'll still need to change your car (I had a mini too!), as you won't get the Bernese in the boot of your mini!Lol But it'll give you more choice with cars, if you don't have to get the large dog, and a large pushchair in the boot ...