Magento Product Customisation

I am in the process of setting up an online store selling swimwear and beachwear using the Magento platform (Community Edition). The store uses the Magento Theme, Fortium - http://fortium.3000themes.com. I have a number of products, including bikinis, and need some customisation done to set up the products in a way that the customer can 'mix and match' bikini tops and bottoms in different sizes or styles. For example, a bikini top in size 10 and bikini bottoms in size 8. Customers can also choose a bikini top in one style and a different pair of bikini bottoms in another style. If the customers wish to mix and match, the individual cost of the bikini top and bottoms is $57 per item. Otherwise, if they want to purchase the bikini set (same size and style) the total cost for top and bottoms is $80. So, it's cheaper to purchase the bikini set. This will always be the default option selected when viewing a product until the customer selects a different size/style Look forward to receiving your quotes.