When do I break out the fleece sleep sack?

Our house is usually around 68-74 degrees. It varies because we have recently shut off any heating/cooling due to the Fall weather. My daughter seems to get hot relatively easily, so I fine with her being in footed pajamas and a cotton sleeveless sleep sack most nights.

Last night was our first frost and her room got to 65! The thermometer in her room is near a window, so it was likely more like 67. We turned the heat on at 68 for her.

When should I bust out the fleece sleep sack? What do you put your baby in under it? What do you keep your house at?

A cold baby is safer than a hot baby, so that is usually how I rationalize things. However, she has never truly gotten cold before.