Playing the E string correctly has been a problem for me as well. I seriously never considered adding a rest until I saw this post. Great idea!! I might try this.
If you're new to playing, it could be your technique. Attacking the E string string can be a problem at first. Depending upon the sound I want, I might use a flicking or rolling motion with my hand. And anchoring my hand with the thumb become less important than the weight of my arm.
I think "the rest" would be more helpful when you're digging into the higher strings and have the thumb solidly placed to deliver leverage.