Starter Home and Proofing Box (Optional)
Temperature is one variable you cannot fully control, but it is an essential element to track so you can understand how changes will affect your fermentation. The temperature of your dry flour, water, starter or levain, and, of course, the ambient temperature in your kitchen, all affect the process and resulting outcome, and since I have spent so much time telling you that temperature matters more than the clock, I owe you some ideas as to how you can influence or control it. Starter homes, proofing boxes, and other temperature-control tools have been proliferating lately, and a dedicated heated box is a simple tool that lets you actually hold a steady temperature instead of just tracking it.
The Brød & Taylor Folding Proofer (~$255) folds flat for storage and holds a set temperature within a degree or two, which is more than enough, and if that is more than you want to spend, your oven with nothing but the interior light on gets you a warm, draft-free box for free, and a cooler with a jar of hot water in the corner does nearly as well, at least for a while.
There are cheaper ways still. Any thermostat controlled seedling heat mat meant for starting tomato or other tender seedlings will work, costs as little as twenty dollars, and is the cheapest fix for a cold starter I know of. Set your starter jar on one and it can add ten or fifteen degrees, enough to wake a sluggish winter culture that would otherwise take all day to peak. I am not going to pretend this is elegant. It is a seed-starting mat from the garden center sitting in a cardboard box, but a cold starter is a slow starter, and slow is the enemy of a predictable bake schedule, so it earns its place in the drawer. I have also pressed into service the type of heating pad I pull out when my back is in its yearly spasm, a clear plastic soil warming mat, and the Kombucha Carboy Heater ($43) I use now, because it's what I have on hand and it works just as well.
I will be honest that this matters more in my kitchen than it might in yours, because I am a polar bear who keeps my house cold, but if your kitchen runs warm, you may never need one, and if you live in a tropical clime, you may instead need a way to cool your dough to keep it in a reasonable production window. When I started, you had to be creative to find ways to do this. The sourdough marketplace now has all manner of tools for this purpose.