Alas, I use a local FMQ and she has wide backing fabric. I am usually not too concerned about the backing color/design.
On the other hand, when piecing the backing (it has been awhile), I think I was told to iron the seams OPEN.
Not sure I remembered that correctly.

IMO, your first consideration should be if you are using a longarm or not. If you're using a longarm, or sending it out to a longarmer, this picture illustrates why you should piece the backing seams horizontally.

https://scontent-sea1-1.xx.fbcdn.net...d2&oe=5982C610

Second, if the look of the quilt was more important to me than the economics, I would pick a busy backing fabric that wouldn't show seams. The ideal fabric would be dark with a small and very busy print. Here's a good example:

https://d2d00szk9na1qq.cloudfront.ne...rge_FD-284.jpg

I took this picture at a show some years ago. I thought it was very inventive of the quilter to make the back so lovely as the front.

This is the front.

I insert a vertical stripe or leftover squares out of the same fabric as the front. Simple 4 patches work vertically. I like to think that if the front were to get damaged, the back could be used to repair the front.

It is very difficult to get a backing exactly centered with a top.

In my opinion, it is less hassle to have a design, extra strips, whatever- in a backing - off-centered so that a couple of inches one way or another will not matter.

Wow, Boston, that is a lovely quilt!

That is a great quilt - I love the way I keep seeing different "blocks" when I look at it.

I would most likely find some corresponding fabric and some blocks and sew a strip down the 44" length (somewhere about 2/3rds across) to extend the width. I love back art.

Good for you! It's really annoying to have a quilt just a few inches too small to fit a backing. I usually buy wide backing to save me the hassle for a small quilt and piece a backing for a big quilt. I do pieced backing this way. The LA can turn the quilt to have the seams going the best way to quilt it.

http://www.reddawn.net/quilt/backings.htm