Yikes a one gallon? Get a bigger one as soon as you can! Do you have any plants in the tank? Or somewhere the Kitty Kitty can hide if she gets scared of your betta? Even though she needs a friend, do not cram another one in the one gallon! Just wait until you get a larger tank. (What you might actually want to do is get a larger tank, at minimum a 5 gallon for the catfish and leave your betta in the one gallon)

Don't get a pleco unless you are sure what kind it is. The ones you find at Walmart and petstores is called a common pleco and can grow up to two feet long. In most aquiriams they only reach around 11 inches to 1 foot, but they need atleast 30 gallons minimum.