Having thought a bit more, I think I'm looking for:
* the existing PCSB to be offered in a durable fabric with subdued colors: probably Halcyon 400d as first choice and 630d recycled as second choice, for flexibility and light weight, and
* a horizontal "Freudian Slip" that would fit inside it: a stiffener that will hold relevant things upright (maybe slots for 2 pens, a phone, and an A5-sized thing on the front side, and an open pocket on the back?).