We just did when he could hold head good and somewhat sit good while being against the seat. We shove blankets in to help support him. He loves being able to look around like that than being in the car seat
I moved mine to the stroller seat. She is sitting up on her own 95% without support and has good head control. We have the evenflo travel system stroller. The seat is also a bassinet
My baby use stroller since 4 months and she’s being fine. She also fall sleep. I think is important the head control
You can use the bassinet attachment. I use that when I'm going to walking around a lot.