Define the roles. If you're wanting to assign titles to the roles, and use them, do so. You don't have to use Master or Mistress, you can use whatever term of endearment you assign to the role.

The things you do in the bedroom are sexually oriented. The ones that are not would be more service oriented, or at least concealed to the point that it wasn't obvious what was going on. Wearing a plug for instance can be done without letting others know what you're doing.

Most of all, keep it fun.