The rule of thumb for welt feet is to add 3/32 to the size of the welt cord and use the foot closest in size. 3/32 plus 5/32 equals 1/4, so that's exactly the right size foot to use.
I use the 1/4" foot for 3/32, 4/32, and 5/32" welt cord, which works good for vinyl, leather, and Ultraleather. If I was sewing thin fabric, I would use a smaller welt foot.
No one lives forever, the trick is creating something that will.