Use Result Value From SELECT As Arg For New SELECT?

 Hi -
 I'm stuck and would really appreciate some help with my stored procedure. I think I am probably really close, but I'm just missing something basic as I'm still fairly new to SQL. Here are the things I need this procedure to do...
 
Query one table with a text string stored in the field called "UserName".  (WHERE cs_Users.UserName = @userName)


Use the UserId value found in the single row that should be returned by this query to execute a second query on a different table. (WHERE traveler_stories.UserID = cs_Users.UserID)

This second query returns all rows that match this UserId and are approved.
Execute the paging logic to return the specified paged result set.
 
Much of this code is already working in other stored procedures. I think I just need to figure out how to use the cs_Users.UserID returned by the first SELECT statement. At present I get the following error which I don't understand "The multi-part identifier "cs_Users.UserID" could not be found." when I try to save the stored procedure. I have pasted the code below. Thanks so much!
 Peter
 

@userName nvarchar(256),
    @PageSize int,
    @PageNumber int,
    @total int = 0 OUTPUT
   
    AS
   
    Declare @RowStart int
    Declare @RowEnd int
   
   
    if @PageNumber > 0
    Begin
   
    SET @PageNumber = @PageNumber -1;

    SET @RowStart = @PageSize * @PageNumber + 1;
    SET @RowEnd = @RowStart + @PageSize - 1 ;
   
    SELECT * FROM cs_Users
    WHERE cs_Users.UserName = @userName;

    WITH T1 As ( SELECT traveler_stories.StoryTitle,
         traveler_stories.PostDate,
         traveler_stories.UserID,
         traveler_stories.City,
         traveler_stories.Country,
         traveler_stories.Tags,
         traveler_stories.StoryID,
         traveler_stories.Approved,
         ROW_NUMBER() OVER (order by traveler_stories.PostDate) as RowNumber
         FROM traveler_stories WHERE traveler_stories.Approved = 1 AND traveler_stories.UserID = cs_Users.UserID)
       
        SELECT *
        FROM T1
        WHERE RowNumber >= @RowStart and RowNumber <= @RowEnd;
        SET @total = @@rowcount;
     


    END