So, update from my experiences...

G7 wanted €43 for a pickup from Gare du Nord to the 3e, which is just silly. No easily hailed G7 Kids cabs on arrivals, so we took a bus from the GdN bus station (very handy to know that place) to our apartment, nearly door to door, and not much longer, given the silly post-€* taxi queues. Loads of space for buggies and wheelchairs on board.

Had less time today so took the metro across town this morning. Easier than I thought, but getting the gate opened for the pushchair was not obvious (even less so if I didn't speak French). Unfortunately I chose a station with loads of steps down, but I'm used to that. There were escalators where we arrived, and I'm used to that too. Plenty space on board the newer trains.

The buses failed us later due to the snow (lightweights!) but the G7 app got us a car seat taxi in a few minutes, which was a huge relief. Price was reasonable, considering.

So, pretty easy, all told!