I had same situation 4 years ago. Got tandem buggy from ebay that time, qasnt really expensive. New baby was at the back and my todler in front like in a stroller and could easily get on a bus if i had to :) Soon after birth my older one got todler bed (which she was very proud of) so we could transfer new baby from moses basket to cot bed. But all depends how much space u have :)
I got a double stroller on Craig'slist cause my daughter will on ly be 15 months. Her stroller is pratically new lol.