I would use the straight seams and make a 5/8" dressmakers seam pressed open to keep it less noticeable and to strengthen the seam.

Straight seams will work, but can you make 4 pinwheels to add at the corners?? Just a thought.

When I don't have enough border fabric I turn to my scraps and/or blocks leftover from the quilt itself. I've added 3 blocks at each corner and/or a couple 3 blocks in the center of the borders. Here's one I did when I came up short for border fabric plus it used up the leftover blocks made by the cut-offs making the main blocks.

I always do straight seams for my borders and they look great!

If your top has an inside border, often you can piece the outside border together matching up the seams on the inside border. For instance, if your quilt had a 3" inside seam, then your outside border would have your pinwheel, a 3" piece of your red outside border, a long piece, another 3" piece of red outside border and then the pinwheel. Does that make sense? Takes a bit more calculating to get the long piece in the center to be the correct length. But, sometimes lining up the seams helps "loose" the seam and is worth it.

Nothing wrong with straight seams, particularly with the fabric in your picture. Go for the straight! froggyintexas

This is quilting! We always do what we need to do. You can do straight seams in your borders, that's the way I learned. I was quilting for about 5 years before some one told me to do diagonal seams. I do what ever I like, want or need to do to make it the way I like. Good luck, what ever you do it will be great.

I haven't read all the posts but I've used straight seams when I was short on material and the quilt police didn't come to my door.

Of course you can add fabric with straight seams on the border - I've done it many, many times, so it's OK.

Go with what pleases your eye.