I use this handrest but missed a soft top part and a other one for more friction on bottom and TPU is the perfect candidate for both. I also reshape the dust cover in order to be more TPU print friendly.
Printing Info for TPU
In order to increase softness for the top part, I recommend 10%-15% Archimedean chords for infill. A textured build plate will help a lot. To remove the TPU easier, it is recommended to heat the bed to 110°C after print is finished.
Glue the parts
I successful glue the TPU to PETG using cyanoacrylate (aka SuperGlue).