Responsive Form with Changing Options

Good afternoon,

My company helps other companies with incorporation and company documents in a huge variety of countries. We are currently migrated from an older site (see link) to a newer one that we are building ourselves with WordPress and Avada.

The one form we have not been successful in replicating is the “order documents” form shown here – https://www.systemday.com/company-document-order.php?jur_id=1

It has to be part contact form, and part shopping cart. The element of the form that I am particularly puzzled by is building a form in which the subsequent options after “Select Country” will automatically alter depending on which country is selected.

The idea is a country is selected from the drop-down list, and the form then will bring up the full list of documents/processes required to incorporate a country there. Customers can then select the ones they need before inputting their own details on the following page.

However I’m not sure how to set this up, as my normal form plug-in Contact Form 7 doesn’t seem able to feature this changing form functionality.

Any help, or suggestions of suitable plugins would be much appreciated!

Thanks
Rob

The page I need help with: [log in to see the link]