IMO from experience you will need a double stroller for longer trips (zoo, amusement park, mall) but not everyday. It really depends on your lifestyle
I have a city select which is a single that can convert to a double if needed. The seats can rotate different directions, you can use a car seat adaptor, buy a toddler glider board (single + board), huge basket it has stadium seating so both kids can see out and one of them isn't sitting on the floor with their feet in your basket (like the Britax or phil and teds). It is great for baby + toddler but pricy ...although it resales very high too.
I also have a side by side city mini GT which is more rugged and what I prefer with two toddlers. It fits through standard doors, turns on a dime, and each kid can nap without any rearrangement.
I am a SAHM and rely on my strollers almost every day. If you have help or going places with shopping carts or your child can walk some people get by with only owning a single stroller. I tried the "wear the baby" method but when you have a toddler throwing a tantrum getting into a shopping cart and almost kicking the newborn in the head (as you lift them into the cart) I rather put both into a stroller and use my basket for my shopping!
Some people go with sit n stands or ones that can convert but in my experience at 2.5 they will still get tired and need a place to sit (or nap) in a stroller for longer excursions, and I still wouldn't trust DD to sit on a board looking at me with a sit n stand without attempting to run off as I am pushing it.