Looking for add-on to include string with tennis racquet purchase

[appriddy]

Hello,

We are looking for an add-on that will allow customers to purchase strings with a racquet purchase and to choose a tension before checkout.  All of the strings would be available within our string category and already products available for purchase separately but we need a way to include this function within our racquet product page.  I have attached a photo of what another website is using to combine the options. 

 

The highlighted area is what we need to implement.