I had to look up Christmas Tree rag quilt -- ooo, not so much the stuff I do but I like the concept very much. And proper grats for finishing a king sized project! So welcome to the boards, glad you found us.
Taking Gemm's suggestion of Sunflowers I found this, which is also a rag style:
https://lifeofadailypainter.com/2017...nflower-quilt/
I usually work in more traditional pieced work, one of the places I go to look for settings and borders and other inspiration is the equilter site for free patterns -- those are usually designed for specific lines with panels, etc. which may no longer be in stock. But maybe they can inspire you to something just right for mom without being too Christmas and a reasonable size for a couch quilt.
https://www.equilter.com/pattern