Non-electric milk frother and cold oat milk. But hot coffee?

Since I don’t have an Aeroccino or any electric milk frother yet, I decided to buy a manual milk frother from IKEA for now. I also picked up Oatly Barista Edition, which was recommended by a Redditor I came across. For coffee, I’ve been using Sweet Vanilla capsules since I really like the flavor.

Before getting the frother and oat milk, I was honestly just mixing instant creamer powder into my coffee.

I mostly drink hot coffee, so here’s what I’m unsure about. Since my milk frother isn’t electric and the oat milk needs to be refrigerated, what’s the best way to do this?

A) Froth the milk while it’s cold (straight from the fridge), mix it into the coffee, then microwave everything to heat it up?

B) Microwave the milk first to warm it up, then froth it, and only after that add it to the coffee?

Or is there another method you’d recommend?

Any advice would be appreciated.