I almost always piece my back. I like to make the back almost as interesting as the front, but with less work. As far as getting them straight, I pin baste and when I put the back down on the table I measure many times to be sure it is straight, then measure again when I layer the top. I can generally get it within a half inch and not noticeable.
One way I find ideas is on Pinterest. Here's my quilt back idea board, but there are many more out there:
https://www.pinterest.com/lesliew333/quilt-back-ideas/