Don't worry it will be fine , I had 13 mths between my second son and daughter, it is hard work but lovely for the kids , they grow up like twins to be honest. mine are older now 10 and 9 , but at the time maclaran did a lovely slim side by side double buggy, small for car storage too. They each had their own space/side and back rests were independant from each other as due to age gaps they were not asleep at same time always. Double shopping space for you is a bonus!! I have seen lots of even slimmer ones nowadays they have got better and better. side by side is lighter up kerbs etc than a one behind the other , but as I say things have moved on alot since my days.
My best investment was a travel cot that was also a playpen and we used to put number 2 in the bouncy seat inside the playpen in the loubge so I could leave the room ok, as my little boy would try to lie on baby or poke eyes out etc