Attributes more that one price variance

Hi

I have a product which has two attributes one is a bed with a cover and the other is an extra cover. Both have different sizes.

I would like to have to drop down options within the product

Bed with cover 14 X 12 ￡x
20 X 20 ￡xx

Extra cover 14 X 12 ￡X
20 X 20 ￡xx

However when I try and set it up in the variable section its confusing. Perhaps I going to have to split the product and setup two products one with a cover and the other just an extra cover on its own.

Your thoughts would be welcome. Thanks