Well it's more often too warm than too cold here, so what I use to keep the starter stable is the refrigerator; the house is a proofing box so when I'm reviving it, the countertop. But 5 years after we moved in here, I realized my oven has a PROOF setting. Which seems to simply turn the light on, lol.

I like to put my starter in the oven with the light turned on in the winter. Sometimes with the door cracked open depending on how hot the bulb gets

I use the Brod & Taylor proofing cabinet (which is also a slow cooker) for my starter and the dough. I find that getting rid of the temperature variable really helps me a lot. When temperature is consistent you can more easily get a feel for how active the starter is. Otherwise it could always be slower or more active or the temperature just lower or higher.