I can assure you, straw bales are better insulation than modern fiberglass. A family member lived on a sustainable farm where they had a 40 foot diameter roundhouse with 25 foot ceilings and an upper loft. Basically, a big volume. It was easily heated, and kept incredibly cozy, by a single woodburning stove.

Additionally, it was fully plumbed with water (though used composting toilets outside), as well as electricity.