You could create a multiAdd to Cart button that adds both items to a buyer's cart with a single click, which we explain how to do here:

However, with that approach unfortunately there's no way to prevent buyers removing one of those items from their cart after they're added, so you may need to watch for that scenario.

Our Development team would need to set up your monthly-fee product for recurring payments with Stripe, so once you've added that product in your E-junkie Dashboard with the price set to the appropriate monthly fee amount, contact us here to tell us the item number of that product we should set up for monthly recurring payments.