Wheat flour recommendation needed

For the longest time I've been trying to make whole wheat bread like the good stuff you get at some of the nicer restaurants.  I've been using KA Whole Wheat flour mixed with either KA AP flour or a higher protein flour like Guisto's High Performer, High Protein.  I usually go with 50% each.

My results look great, but the consistency is best described as "sandy" or "gritty".  The crumb doesn't have a soft & fluffy consistency.  My routine goes something like this:

• 500g four (50/50 whole wheat & AP)
• 400g water
• 50g active starter
• ~12g salt

I mix starter & water, then add all the flour.  Let it autolyse for 45 mins.  Add the salt and start a stretch & fold routine for the next 3-4 hours.  Put the dough to bed overnight in the fridge.  Shape the next morning and let it rise for a few hours.  Bake at 450F for 45 mins.

Thanks!