Some national banks (BoA, Chase, etc.) and credit card companies (Discover, Amex) offer a one-time card number for online purchases (if memory serves, PayPal used to offer it as well). The process is simple (at least in my experience): either online or over the phone, you arrange with your bank the purchase amount and they will give you a credit card number that is only valid for that amount, for one transaction, and usually only good for a short amount of time (a few hours). If the worst happens and someone intercepts your credit card number (virtually zero chance when dealing with a reputable vendor), you would, at most, be out the amount you and your bank agreed that "card" would be worth.
Most credit card theft occurs when someone else contacts you and solicits your card number (e-mail spam & scams), or when the company you purchased from suffers data loss (TJ Maxx had this happen a few years ago). Since you are contacting the seller of your own accord (to purchase goods or services), the first option is out. Because the card number is good for only one transaction and the merchant will have already charged your purchase, the second option will not result in a loss to you- the thief will have a credit card number that is no longer valid.