Link a Dropdown/Radio Button selection to Add to Cart

Hello all,

I am putting together a form for my ecommerce site and at the very start the user would select a service they would like before completing the rest of their information on this page:

(There are currently two service selection options, a dropdown and a radio button selection which is just to choose whichever works best at the moment!)

So far, each selection is its own product in my ecommerce product page, what I would like to do is, based on whichever option is chosen from the radio buttons or the dropdown, once the user hits next it would take them to a checkout page to fill in their info for their chosen service.

Would anyone be able to advise or recommend a way of linking these two?