Want to try sewing? its not as easy as asking shopping leads , but not that difficult..
average small panniers are 12" tall .. might hang rather low, y/n ?
alternate the low rack can support a single large pack sitting on top of it
it has been a touring option others have used .. full back country packs..
the rack for your chosen bag from the seller you found
https://www.modernbike.com/ortlieb-r...1-only---black
There are options to fit a bag on the seat post , like the Xooter cross tack ,
or some of Carradice SQR, and Klick Fix
& top of that rack with its own QR mount
Ortlieb has one , for your laptop hauling...
....