Add capability to isolate manual membership payments

My org wants a way to track the success of our appeals at getting people to become members or renew memberships during any given period.

The problem is that, in Civi, there is no simple way I can find to reliably distinguish between a membership payment that is made manually and one that is done automatically. We don't want to consider automatic payments in our analysis, because they weren't influenced by our appeals, but we can't find a way to filter them.

My first idea was to use the field "Is Recurring" in Find Contributions, but it seems to include a category of payments that shouldn't be included, at least for my purpose. This category is payments that are the first in an automatically renewing membership, during which the member checked the box to make the membership renew automatically.