The guest requirements for the long term booking are different than the short term guest. Is this your first long term booking? I am not sure why you post that these guests are germaphobes. Stains are never good, but mostly not an issue with a short term guest who does not strip the bed.
Since you are okay with buying a new mattress/boxspring set for your own use, no problem about that.
People have different thresholds of sense of safety. New is often experienced as not safe. What can you do as a host to help these guests get over the "new or unfamiliar" factor? You are hoping these people will stay for 2 months. Do not use the same hosting style as the for your short term guests.
Payment is a whole different issue. Have you looked at the Air BNB policies about payout and cancellation for long term? Different than the short term policies.
BTW, your cleanliness rating is substantially lower that all your ratings. Do you have any idea why?