All of the above. Literally. New windows and doors, insulation, heating changes , etc. Plus a few more things like vinyl siding over the concrete block and metal roof. It was concrete block, shingle roof, doors with a lot of glass, steel frame casement single pane windows and not an ounce of insulation of any kind.
It's now vinyl sided with nearly three inches of foam board (inch and a half outside, 3/4 inch inside) and drywall added (exterior walls are close to a foot thick overall), metal roof, several inches of insulation in the attic, thermal windows and doors ..... and on and on and on ...
All new wiring and plumbing too, plus all LED lighting.
I was going to start a similar thread, but I'll add this here.
Digging through old files and papers, I pulled all the bills for propane. The first year or two before I got a lot of the work done, I was burning close to 700 gallons a year. That started to come down as progress was made.
I'm down to getting 200 gallons that will sometimes last more than one year.
I'm giving up on the wood burning though after this Winter, so we'll have to see what happens.
This year, I've used very little heat over all. I still have most of that last 200 gallons from last Spring and I've only have one wood burning day. I'll get another 200 after the first of the year so I'll have some in case the generator needs it.