You should post this question on the notaryrotary.com and gomobilenotary.com boards.  Those are the two most often posted boards for notaries public and notary signing agents.  I am not the best person to answer your question.

There is E&O insurance for your actions as a public official; i.e., you function as a notary public.  Not too high priced depending what you are notarizing and easy to get.

Then there is E&O insurance coverage from your actions as a document courier & non-attorney signing agent who is entrusted with a lender's customer's date-sensitive loan documents and personal financial and identity information.  Costs vary by carrier, state and the volume of business you are doing.  You may need to shop around, which is why you'll get better answer on the other boards.