@Ovidiu, you only need one membership level for the whole thing which is the “Digital Subscriber”. Members who sign up for this gets to read the protected content (digital version of the magazine) on your site.
You can simply create a subscription button for the payment of the paper version. The following post explains how you can create any type of subscription button with the WP eStore plugin:
when someone orders a paper version using this button they get the paper version delivered (weeky, monthly, yearly or whatever) as long as they stay subscribed. No need for any membership for them cause they will never need to read anything online.
If a digital subscriber want to get the paper version delivered too then they just have to pay for the paper version using this subscription button. No need for another membership level since they can already read the digital version.
let me know if this makes sense.