I got the arm straps done with the help of my mom. We used premade bias tape from Hancock Fabric (like Joann). The specific information is that it was 1" wide brown bias tape for quilting. This means that it is a bit thicker than some of the other bias tape there. The width of the bias tape was pretty much spot on and at a cost of under $2 for 3 yards that's not too bad. We ended up having to get a second package to finish it.
Going along the lines of planning it out first, we happened to have a piece of ribbon from a gift that someone gave us for Christmas that just happened to be the right length to measure everything. The straps consist of one long piece across the entire back, two loops from that straight piece over the shoulder, and then two loops that go around the outside of the arms.
The actual sewing was pretty straightforward since we just had to stitch the sides of the bias tape together. We were able to use the entire 3 yard length for everything excluding the loops around the outside of the arms. The forward loops and the straight back were stitched together with the tape folded over at a 45 degree angle.
In the reference images you can see two buckles in the front where the outside loops attach to the forward loop. We decided to make this an actual functional loop that would allow for adjustment of the outside loop. The buckles were bought at Hancock for about $3 and it was put together much like a shoulder bag strap.
I think the straps came out pretty nice and from a distance it actually looks a bit like leather.