somewhere I saw how you make a continuous bias strip out of 1 yd of fabric.
Hmm trying to think it out. Maybe if you started with a longer length of fabric, the same as the WOF, you are going to use it all anyway, on your various projects.
cut the selvedges off your fabric. cut fabric in half diagonally.
now you have 2 "half squares" sew them together into a diamond, you know, the straight edges of the left one forms the left side of a "T", the right one forms an "L". sew the up & down edges together. The bias edges are to the left & right.
now bring the other straight edges together into a tube, offset it the amount you are cutting. So there's a leading "rabbit ear" and a trailing Rabbit ear, both the width you want to cut. you cut along the first bias edge, and end up at the trailing rabbit ear bias edge.
cut it on the width you want. The cut will spiral around the tube, on the bias. As big as this tube is, if you have a 12 or 18 inch mat, slide it into the tube & ruler cut it.
Since you are only using black, and you need a variety of widths, you could make one of each.
If you dont want to do that, the thing is bias, anyway, I doubt it would cause you any problems if you switched to different widths as needed.