Safe heat when there is no electricity?

Hi, I found a gap in my planning this last week when our power went out for about ten hours. We had plenty of light because the sun was up for most of it, and candles and battery packs for phones, but because it's March in Minnesota it did get chilly. Thankfully we had the house reinsulated last year, so it never got below 55. We mostly just huddled on the couch under a couple blankets.

That said, had the power outage lasted longer, or been primarily at night, what would everyone recommend for a safe electricity-less heat source indoors? We don't have a fireplace, or a wood or corn burner, or a safe place to put one.

Thanks all.

Edit: Thank you all! I'm not sure about a propane heater in the house, with chaotic kids and cats, but I hadn't thought about putting the tent up in the living room. I should also get a bunch more mylar blankets. Next power outage, we'll have a "Grand Camping Adventure" while we wait for the good folks at Xcel to fix the lines.