Hello and welcome!
I’m not in BC so maybe a local could help to chime in on local issues and whether a two brood box setup is something to consider.
However, there are a lot of questions tucked in your post…
Why did your hives not do well in the prior year?
Generally, adding a super (flow or otherwise) can be a good swarm control measure.
Adding a second brood box won’t necessarily require you to delay adding a flow super but your bees will need to build out the extra box.