It is safe, as long as the blanket is not too hot. Keep it cooler, and try not to cover up the cord leaving the blanket at the foot of the bed. Make sure that the blanket is UL listed, if in the U.S....
"Down blankets are definitely thicker, because they contain things inside them like goose down feathers. Knitted blankets are thinner, but sometimes can feel warmer than a down blanket because one...
Blanket is called Blanket because Michael uses that term to convey protection, comfort and support. He wants to "blanket" his children, as any parent would. He explains the name in the Martin Bashir...
You could have both on the bed; but certainly the comforter would be decorative only, since the electric blanket would keep you warm enough. There would be no hazard with using both, however.