I've seen countless graphite/pencil artists use a transparent plastic sheet that they place their hand on to prevent smudging of the picture they draw. Exactly what is this called, and can you buy these?
I think you can buy any generic plastic sheet for that purpose. Sturdier plastic - acrylic, PET - sheets will probably work better as they are less prone to movement.
Many artists use regular paper sheets to rest their hands on while drawing.
If you really want to diminish the risks of smudging, you can tape both your drawing and the plastic sheet to your working table.
A great alternative is to use bridges:
The great advantage over sheets is that they don't need to rest on the surface, which will prevent any accidental surface damage. They are also relatively easy to craft yourself (allowing for customization).
On the other hand, they will slightly impede your hand movement, and need some getting used to.