CHECKOUT FORMS - customer ability to add or delete products like shopping cart

I would like to add a request for the tech team to add the ability to mix and match items (like a shopping cart) for the checkout system. I sell 3 types of consulting and ONTRAPORTS current system requires that I have a different checkout form and page for each. I wish it was simpler and I could list all 3 options and they could select which one to be charged for on the same form.