Baby isn't born yet so this is not currently an issue.
My right boob is a slacker boob, it was the whole way through my first born's breastfeeding journey and we supplemented with formula.
I since found out I had thyroid issues that may have impacted my supply, but even now at 36 weeks pregnant I can produce colostrum from my left boob, but only get maybe a drop out of the right. I suspect that even with my thyroid issues resolved I'll be faced with the same issues of undersupply, or at least be relying mostly on lefty to do the heavy lifting!
My question is would you start with the slacker boob at every feed in this instance? I'm scared that doing this everytime with a newborn will drain their energy for very little return in those early days so I'm not sure if it's a good idea.