Just because there's never been a problem doesn't mean there won't be. You can get one for $30. It's honestly irresponsible to keep animals without providing proper care.
I'm sorry, but it's your pet, your responsibility to do research. It's nobody else's job care for your pet. A quick Google search on snake husbandry will show countless sources which talk about the importance of a thermostat. Just reading a care sheet or two isn't doing proper research (not implying that's what you did,I just see it way too often).
We owe it to our animals to provide proper care. They don't get a choice and rely 100% on us for their survival.