Inspired by iheilala's Kitchen spool holder design, -take a look here: https://www.thingiverse.com/thing:2470371
I drew a similar holder. Made easy-to-print, -no supports required.
For paper towel center opening: 35mm
Made for shelf thickness: 18mm
The top of the shelf clip is tilted 1 degree down for stronger "pinch" on the shelf.
In the download its included single piece (which you have to duplicate and mirror one of them in your slicer), or you could just print the STL with two pieces already mirrored.
Perimeter shells: 5 (gives more strength)