How can I add upgrade options to a subscription product?

I am struggling finding a way to add a subscription product that includes upgrades. I work for a Home Warranty company and we can add sorts of options on top of our $49 a month plan.

However, I cannot figure out a way to do that.

Can anyone assist me?

Hi, do you mean that you want to simply allow your customers to add additional products (add-ons) on top of the base $49 plan?
This is an option in the Seal Subscriptions app which is also available on the free plan.

Or do you mean that you want to have some kind of a guided process where the customer selects the desired addons?