You might be able to find traditional Catholic items a la Native American in theme by contacting any church on Native lands, or mission schools to Native people. eBay, sad to say, is also a source; I saw (but could not afford) a stunning Navajo turquoise beaded rosary done in sterling silver by a Navajo silversmith.
Yes, as long as you don’t believe the items have any real power, it’s okay to use them as decor. However, do be careful in not adopting any items which do have real special significance to that culture, and be aware that it is illegal for nonnatives to own any items with real eagle feathers in them. Also, be aware that many items that are being sold as “Native American” items really were made in sweatshops in China!
While you are at the task of decorating your home, you might want to say a few prayers for the cause of Blessed Kateri Tekawitha, the Lily of the Mohawks, who lived near the Adirondack region of New York State at around the time of the Jesuit Martyrs (late 1600’s.) If canonized, she would be the oldest North American Saint who was born on these shores. Her simple faith, and courage in dealing with the abuse of her people when she refused to marry, instead dedicating her life to Jesus, is an inspiration to all of us Catholics of Iroquois heritage. Her canonization is just one miracle away, and she has been lingering on the “blessed” list for eons now!