What to do if your dough won't double in size even in the warmer area (and your baked goods are dense) - If your dough doesn't double even in the warmer area for either the bulk ferment and/or the second rise, your starter is too weak to ferment the dough even in a warm environment. Don't worry this can be fixed!
To fix this, you will want to leave your starter out on the counter for 2 days and feed your entire starter jar every 12 hours at a 2:1 ratio of unbleached flour to filtered water (example: 1/2 cup unbleached flour + 1/4 cup filtered or bottled water, double this or cut it in half depending on how much starter you have, only fill your jar half full). Remove some starter before doing the feedings to make room if needed.
Make sure you're using unbleached flour and filtered or bottled water to do this. If you don't, it will affect your starter strength. Reverse osmosis water (or any water that uses salt in the filter) can make the starter weak.
By doing this feeding every 12 hours will strengthen the cultures in your starter for light and fluffy breads and treats. After the 2 days, you can go back to feeding it like normal. Be sure to use the 2:1 ratio feeding from here on out.
Sourdough Baking Disclaimer - I feed my sourdough starter a 2:1 ratio of unbleached flour to filtered water, this creates a 50% hydrated starter. If you feed your starter differently or it isn't active before you start making this recipe, results may vary.