In a large skillet over medium-high heat, brown the Italian sausage until fully cooked, breaking it into small crumbles. Drain excess fat and transfer the sausage to the slow cooker.
In the same skillet, cook the diced bacon until crisp. Remove bacon with a slotted spoon and transfer to the slow cooker.
Add the diced onion, minced garlic, sliced potatoes, chicken broth, water, red pepper flakes, salt, and black pepper to the slow cooker.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours, until the potatoes are fork-tender.
Stir in the heavy whipping cream and the chopped kale.
Cover and cook for an additional 15 to 20 minutes on high until the kale is wilted and the soup is thoroughly heated.
Taste and adjust salt or red pepper flakes as needed before serving.