Putting Zero At Front Of A Single Digit Variable?

I am retrieving the current month and setting a variable accordingly.

Code:
DECLARE @currMonthNum INT
SET @currMonthNum = DATEPART(MM, GETDATE())

My challenge is that at a later point I want to use the @currMonthNum value to 'build' a date in the style yyyymmdd and the variable is only one digit for the months January to September (e.g.: 1 to 9). For the months January to September I need to pad the variable with an extra zero (e.g.: 01 to 09).

Here is my attempt to do this...!

Code:
IF @currMonthNum IN (1, 2, 3, 4, 5, 6, 7, 8, 9)
SET @currMonthNum = '0' + CAST(@currMonthNum AS nvarchar)

Unfortunately this does not give the desired result of two digits, however ironically if I add a + '0' to the end I get 10 to 90! It is like the 0 at the front is simply being ignored.

I have also tried setting the @currMonthNum variable to an nvarchar type before performing the character addition as well attempting to use the CONCAT command (however I don't think that CONCAT can be used when setting a variable).

how to display a zero in front of the months that require it?