For this type of products, Configurable products type is the best option. First create the attribtues as shown then create the configurable products. Actually this can be set while you create those attributes like blouse size, length and customization. Go to the admin panel. Catalog->Attributes->Manage Attributes. Here search for your attribute that are using for those COnfigurable products. Then after edit those attributes and then you can see a field like "Required Values"-> Make this as Yes. Attaching a screenshot for ur reference.
Edit the other attributes as you required. Then make an ReIndex management and clear the cache. Refresh the frontend...Hope this helps.. :)