I’m not a fan of cold, but neither am I fond of humidity. I do better with drier heat, but even as heat tolerant as I am, there are limits.
I know they can be stupidly expensive, but the Dyson cooling fans are utterly brilliant. I don’t know if you have them in Australia, or if there are similar fans, but they are far more energy efficient than air conditioners and work extremely well. A friend of mine got one for her lake cottage, and almost never uses the actual wall mounted air conditioner she had put in. The Dyson cools the place very well, and it’s comfortable—not freezing like air conditioners can be. They’re also portable, so can be moved from room to room. It’s a thought, to help you and mum. If not for this year, think about it for next year. You might catch sales at the end of summer.