I have a method for turning certain words into bizarre strings of characters and numbers. I remember the method and feel perfectly safe writing the original word down in relation to a given site.
Shopping online is just as safe as shopping in real life. I have met more people who have had their bank information stolen through a corrupted ATM than through a corrupted server, in fact. Look for the little lock icon and stay away from fly by night companies. Also, keep your antivirus software up to date and if you hang around seedy parts of the internet, get yourself some
protection. Theoretically, online shopping should be safer because a real person should never even see your personal information. Meanwhile, in real life when a person inspects your credit card they can memorize every digit of it.
As for getting your password back, I would recommend trying to contact Yahoo through conventional means if it is really important, or just moving on otherwise.