Hannah,
You never did say your reason for building a tiny home, is cost savings, mobility, because there is just two of you?
if you buy a plot of land and build a home from non traditional building materials you can save a huge amount of money over the life of the home.
https://www.thenaturalhome.com/passivesolar.html this waas the site that got me into sustainable living solutions.
Tire homes or straw bale homes are also very inexpensive, some basic framing in the case of a straw bale then fill in your walls by stacking up bales.
Any High Thermal Mass home should reduce your heating and cooling costs and if you add a rocket mass heater with pizza oven, not just for cooking pizza you know.
