Welcome to the forum!
It is definitely possible to nurse on just one breast. Think about moms of twins- that's basically one breast per baby, right? While one-sided nursing is possible, it's usually better to have 2 breasts in service. That way you're less likely to get lopsided from one breast getting lots of stimulation and making lots of milk while the other gets little and makes little, and you'll have a working spare breast in case there's some reason you can't nurse on the baby's preferred side.
I think it makes sense to continue to pump the unused side, removing enough milk to feel comfortable. I wouldn't take more than a couple of oz at a time, because 2-4 oz is generally all a baby eats at a feeding and taking more than that will perpetuate the oversupply/engorgement problem. The breast produces as much milk as is demanded of it, so take 2 oz and you'll make 2 oz again, take 6 oz and your body will replace that 6 oz. The more milk you leave sitting in the breast between feedings, the more your supply will decline. Simply putting up with the engorgement would be the fastest way to get supply to go down, but not the most comfortable, and engorgement increases your risk of plugged ducts and mastitis. So if you can bear to continue to pump, or better yet to hand express, I would continue to do so.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"