You mentioned that your son has "left the nest"...are you still close? If so, just use his address as your residence...heck, he used yours for years:)
As mentioned, you can have mail forwarded by an agency, or just ask your son to put the important stuff into an envelope and send it to whatever CG you are staying at....or General Delivery at the local USPS Office.
Having an on-line bank might not be a bad idea either. I'm not sure the SS is gonna want you to use their card as a savings account....assuming you don't use every penny every month? With a national bank (Wells Fargo, Bank of America, etc) you can do all your banking online, and have your SS checks direct deposited, and direct the money where you want...savings or checking/Debit card.
There is tons of information on this forum, so do some searches...
Good Luck:)