I'm considering the valco snap duo.
I have an old Graco uno2duo stroller (single to double stroller) that I'm not sure they make anymore but there are lots of other single to double strollers that look nice! But I also got a Jeep wagon last summer and it has a carseat adapter to use for infant carseats, that I'm super excited to use this summer. The one I have is only a 2 seater but my girls are pretty petite so I think they can fit easily side by side (they will be 4 years and 21 months when Baby is born).
Honestly I’m also considering a wagon but there are options to attach a little ‚hammock‘ to your stroller so your toddler can sit and relax while bby sleeps in the bassinet