Different checkout process for different products?

I'd like to be able to either:

• add a second mailing list sign up, or
• add a step in the checkout process (which would invite customers to give permission to subscribe them to a second mailing list)

But I want to do this only for 2 SKUs, and not the other SKUs available on the site. Is this doable? If so, how? I see how I can add a form to the product page, but that seems a pretty clunky solution. I'd strongly prefer something that happens after the product is placed in a shopping cart.

I'd be very appreciative of any suggestions!

Thanks in advance.

You can create custom product forms for customers to complete when they purchase these two SKUs.

https://support.squarespace.com/hc/en-us/articles/205811218-Creating-a-custom-product-form

Thanks. We were hoping to avoid adding a custom product form because it interrupts the checkout process. I think what we're going to do is to use a custom form in the checkout process, and just make it available to all of our users (who may opt to sign up for the mailing list or not).Still open to other ideas.