You could open a separate bank account for dealing directly with CoinBase. Only keep a small amount of cash in the account to limit your risks. For US bitcoin users it is really the most convenient method to purchase bitcoins.
I think this might be your best bet, TC. You can use the same bank you use now and open a second account with them. Any attack on Coinbase would only subject that one account at the bank; your main account would still be safe.
With two accounts at the same bank, you could easily transfer funds online from one account to the other to purchase Bitcoins through Coinbase. Doing this all online would make it easier to transfer only the amount needed for your purchase, so you won't have to worry about having leftover money in your account that could be taken if the account were compromised.