No HVAC here.
Propane space heaters as needed during the winter, but I think the last time they were on was early April.
We do have a couple of ancient A/C window units but they are so ineffective that we only turn them on if the inside temps go over 100F and stay up there well into the evening hours. Which can happen in July/August here. One year, a candle melted and dripped down the side of the fridge, so I do pay attention now.
Acclimatization is definitely a thing. It's all relative. Right now, 85F feels comfortable, we're seeing some lower 90s, but it's going to get much warmer. By October, 85F will feel freaking chilly and I'll probably wear long sleeves the first few days until I get used to it. I've also found the first two weeks of heat are the worst.
The big downside right now is having to sit in an office all day at 72F. This keeps me from acclimatizing to the heat well. You would think that AC would be a relief, and it feels great, but in reality it just makes it harder.
I practice thermal sailing - opening/shutting windows, using fans to direct air flow, etc. I also plan activity for early or late, and lay low between 2 and 4pm. Summer is the time for low-heat foods; stir fries, salads, cold soups.
Nights usually drop into cooler temps, so sleeping with windows open is very pleasant and I usually use a blanket year-round.