Hi op,
I had a Weimaraner, now sadly passed away, so she was big and strong, but l had a robust Phil and Teds stroller with one dc in front, and one Dc under in the bassinette, when Dc 2 got bigger l swopped the basinette for a second seat so they were one behind the other.
It replaced my gym membership for a few years! I found it easiest to get up with dcs at 7.30 get them fed, changed and dressed, and then get right out with D dog .
My dog was soon very good at walking alongside the stroller, and l would let her off at a large enclosed park, and throw some balls for a while, then walk back, it was fine, l did it daily for 3 years.
With one a sling may be fine but l have a back injury so couldn't carry in a sling, plus they soon get very heavy...
Really you will be fine Op, it is so much easier alone than with a destructive partner like your now ex, you make the routine to suit yourself, and baby.
Cheering you on from here.