I don't know how "light" or "fluffy" this is, but I use a modified version of
Grandma Rosie's Fabulous Challah.
Here is what I do:
mix 1/2 cup warm coconut oil, 1/2 cup sucanat, & at least 1/2 cup whey. Start adding freshly ground wheat (I've used either spelt or hard white wheat) by the cupful - after first cup, add 1 tsp yeast and 1 1/2 cups potato water. After 3rd cupful of flour, add 1 T salt. When it starts to look thick, add 4 eggs. I am not really sure how much flour I use - I just stop when it looks right. (sorry!)
I keep my liquids at the 2 cup point, regardless of how I divide it...maybe I'll use one cup whey, one cup potato water, or whatever...
Then after I'm done kneading, I put it in the oven overnight - with the light on if it's cold, otherwise I just stick it in there to keep it off my counter. In the morning, I form it how I want it and let it rise again (slowly). Usually it's ready to bake that afternoon, so I get about a 24-hour soak in for this.
I've tried it with no added baker's yeast and extra whey or kefir instead. Tasted fine, but it was a lot less convenient for me...it would inevitably take longer than I anticipated, and be ready to bake just as we needed to go somewhere etc.

I would imagine you could sub sourdough starter for some of the liquid/flour. I use potato water to feed the critters in the dough and also because I hate to throw it away when I make the occasional batch of mashed potatoes.
I don't usually do much to shape the dough. It's easiest for me to just dump it into the bread pan rather than braid the dough, though I have on speical occasions. I have a phobia about dry bread though, so I tend to go a little lighter on the flour (resulting in a softer dough) and it gives me a better result to just put it in the loafers.
My family LOVES this bread. Even my mom, who is a bread snob, was pleasantly surprised that a non-breadlover like me could turn out something tasty. heeheehee
hth