Are body temperature PTC heaters a thing?

[Mr. Scram]

For a small project I need to heat something to approximate body temperature. As I want to keep it as simple as possible, I'm thinking of PTC heaters. Just hook up a source and you're done. I know they're not the most accurate, but I don't think I need very accurate temperatures to make this work. The lowest temperature PTC heaters I can find are 40 degrees Celsius which should work fine, but I'd think there would be some kind of market for body temperature analogues. Am I just looking in the wrong places or am I barking up the wrong tree here?