Conditional fields CB subs registration

hi, I have a problem with registering and upgrading users via cb subs.
I have 4 subscription plans and a couple of products (books) on the site. The first plan is free and during registration I ask you to enter only your name, surname, email and password. The second plan offers only digital products and therefore the fields for registration and/or upgrades are the same. The third and fourth offer physical products (books) included and therefore I also ask for the address and telephone number. 
The problem arises if one wants to buy just one book or if one wants to upgrade.
In the first case I register for the free plan (first) and add the book to the "cart" but this way it doesn't require the address. The same thing happens for an upgrade from a free plan (or second without physical products) to a paid plan with physical products (third or fourth). In this case, those who are registered are not asked to enter their address.
How can I solve it?

It's currently not possible to ask for additional information during the basket payment process without writing an integration to add such fields. We'll be implementing custom fields functionality for purchases in a future release, but for now it requires coding. As CBSubs was designed as a subscription manager and not necessarily a store front for physical goods it doesn't have explicit shipping address features (something we'll be exploring in a future release). Personally I would just turn on the invoice address feature in CBSubs > Display > Invoices and you can use that for collecting shipping address and while it's intended to be for the billing address you could use that information for shipping just fine.

Ok, thanks