Re: SD NP dough difficult to handle

That dough needs to be stronger.  There are a number of ways to do this, some involving your initial mixing technique, but also a series of stretch and folds or coil folds spaced out during your bulk rise after the initial mixing can help you tremendously.

What Scott said.
I started doing stretch and folds during bulk ferment and it was a game changer. This chart was useful..
From section 7.8 in here https://www.the-sourdough-framework.com/Wheatsourdough.html#dough-strength