Cem

That is a much better way of putting it than I managed.

If you do decide to control it, the cheap version is genuinely cheap and it is what most people end up with.

An inexpensive plug-in temperature controller with a probe. It switches a socket on and off to hold a set temperature. Two configurations:

For cooling, plug in any old fridge. The controller overrides the fridge's own thermostat and holds it at whatever you want: fermentation temperatures are far warmer than a fridge normally runs, so a second-hand one is fine and it will barely work.

For heating, plug in a small seedling mat or a low-wattage heater inside an insulated box. This is the version for a cold flat in winter.

Either is a fraction of the cost of anything sold as a fermentation chamber and it does the same job.

The intermediate options, in ascending effort: a cool box with a bottle of frozen water swapped daily, a cardboard box lined with insulation to damp the swing, and a bucket of water around the jars: water has a lot of thermal mass and slows the swing considerably for nothing.

Start with finding the stable spot. For a lot of people that is the whole solution, and the controller is what you buy when you want a specific temperature rather than merely a steady one.