Product type

Im currently struggling to think of the best way to set up an existing product.

The product on the joomla site is all hard coded.

The product is a, lets say cuboard.  You can buy the cuboard just on its own. OR you can buy the cuboard with a door. Door has many many styles, about 20.

Doors can also be purchased seperatly.

So The product cuboard call it "CB101" is a simple product currently,  I was going to add the doors as product attributes, but that seems wrong.

Is there a way to display the CB101 with the option of a door as a drop down list?
(I though you could achive this via grouped products, but im second guessing my self)

You can do it with either product attributes or grouped product.  If grouped product, then you'd create two simple products - one with and the other without doors.

I guess the best for you is to use a product attribute for the doors type and associate each door product to the corresponding attribute value as explained here