I have been using the wide backings on my quilts and you are right they are not the same thread count as the 44'' goods. They work well on the backs tho. I have found Moda 108'' in the same line as the quilt I was making . I have used the wildflower serenade 2 line and they had backing to match in the 108''. Ask at the quilt store you frequent or check Hancock's of Paducah. They sometimes have it on sale. I haven't used it on the fronts yet as both times I had the tops almost finished when I found the backing. You do save money buying the 108' because like it was stated you don't need as many yards because you don't need to piece it.
Good Luck
Suzy