Mr Smarty Plants has memories of chasing an errant golf ball under a beautiful blue spruce that had branches extending to the ground and finding the area inside devoid of life, just needles! Be sure that if you are trying to encourage a ground cover that the tree is raised a bit so that there is a reasonable amount of sunlight available!
It looks like you have a good number of choices of low plants. We have a collection of native Wisconsin plants, and this collection is searchable. I chose plants listed as 0-1 ft. tall and then read the plant record [under “Growing Conditions”] for acidic soil. 14 plants were returned by the search and most of them tolerated acidic or circumneutral soil.
These five species have a decent groundcover aspect and react well to acidic soil:
Asarum canadense (Canadian wild ginger)
Cornus canadensis (Bunchberry dogwood)
Mitchella repens (Partridgeberry)
Uvularia sessilifolia (Spreading bellwort)
Viola pedata (Birdfoot violet)
Whats the best source? That’s a bit hard to determine from Texas! I’d encourage you to investigate Wildflower Center Associates and, once again, you can search that list for those close to Sheboygan. I found Rolling Acres Natural Landscape and Kettle Moraine Natural Landscaping at the top of that list. The Wisconsin Department of Natural Resources has a publication "Wisconsin Native Plant Sources" that seems ready made for this question. Other more local good information sources include the Botanical Club of Wisconsin and the Sheboygan County Univ. of Wisconsin Extension Office.