In Swedish too, so this is not an idiomatic expression, rather it seems like a reaction to the usual saying.
Interesting. Never heard of that. It is a bit like "my home is my castle".
I've never actually heard "My body is my temple", but it clearly stems from the Bible which teaches that Christian bodies are "temples of the Holy Spirit."
Yes, that's exactly where the English phrase is from. I mostly heard it in church.
In Swedish, would it be more common to say "Min kropp är mitt palats" or "Kroppen är mitt palats"?
Min kropp as you specify thar it's your body and not the human body in general.