Hello,
I was in the same boat as you when we had our third child. I think it's important for kids to walk as much as possibly slowly eliminating the stroller when they reach two years old. This wasn't an issue when our middle child was born because we used the same stroller as we did with our first daughter. Our oldest is very well-behaved and not much of a concern. But when our third was born I was concerned I'd never be able to leave the house because our middle child (2 years) is a bit of a handful and not like our oldest. I needed to be able to restrain her in a stroller if I needed and be in control of at least two children.
I went online and fell in love with the sit-n-stand stroller from baby trend. It's not majorly huge like the full two seater stroller and allows the older child freedom of either sitting or standing and you can strap the second child in if needed. This also takes an infant carrier as well for the new baby. Works great! I even got free shipping. It might have cost around $400 or so but I also bought a new infant seat as well that matched the stroller, and happy that I did. It's great and works ideal for our family. My middle child (2) likes to use the platform as a scooter and she pushes her one foot on the street while holding on and has the other foot on the platform. This stroller allows her to be as active as she needs or offers her a seat to sit and watch when we are out and about.
Let me know if you'd like more information on this stroller.
Best of luck with your second child soon entering this world.
God Bless, L.