A Boolean data type is true/false or 1/0. For your setup, you're best bet is to use a text data type with a length of 2 OR an Integer data type.
If you use integer data type then when you go to display the values saved, it will display the 1 or 2 or whatever value the user selects in the dropdown list.
If you use a text field, you can store the actual text simply by not adding the value before it. So your setup would be Text data type, with a length of 20 and the dropdown list form conrol. In the list of options simply add:
This will then store that text as the value.
Another option is to use Categories.