If by "cold ferment" you mean refrigerator, my suggestion would be to stop using the refrigerator.
If you need to use the fridge for timing (maybe you need dough in a week, but you can only make it today), it's a great tool. Otherwise, I believe room temp (60-80F with about 65F optimal) makes a better dough. You will develop more flavor in a day in this range than in a week in the fridge. In either case, there really isn't anything you can do to get a "sour" flavor from ADY, IDY, or CY. The biochemistry just isn't there.
I'd shoot for a dough that ferments in the 63-65F range for 48hours - maybe 0.03% ADY.
If you bump up your temp and lower your cook time, you will improve your tenderness. Even getting it down by 30 seconds will make a big difference.
You might also try a point or two higher hydration and see how it compares. If you like it, go up a little more.