When it comes to our selection of free Shopify themes, you have a lot of great options to go with!
While you could potentially find a developer to alter the code and change your dropdown variant option to buttons, it might be quicker and easier to switch to a theme that already has this option built in. Check out the Shopify theme Dawn, for an idea of what that looks like.
The style and presentation is very close to Debut as well. Check out the example image below:
Do you have any other requirements in a theme? If so, we can always take a look and help you narrow down the options to find the best fit. Let me know!