S.K.
You don't need a double stroller right away. My second was carried in a sling for my convenience for the first several months anyway. Until they are able to sit comfortably on their own they never seem to like the stroller!
My first daughter was 23 mos. when my second was born. I carried number 2 in a sling or baby bjorn until she was about 5 months. By then my first was old enough that she hated sitting in the stroller and I bought a Peg Perego Pliko P3 that allowed my oldest to stand on the back.
It worked very well for us.
Good luck!
-S.