Mixing vertical image slider for main items and horizontal slider for per item sub items

I am having a bit of a hard time to find a good solution for the following situation: As a user I'd like to add a section to my page. First you will need to choose which type of section you want (in the sketch it is on "Header") then you can choose out of the designs of this type. In addition, each design has variations. The total number of designs and their variation can sum up to 30 items and more.

How is it best to present the choosing possibilities?

Imo it would be best to choose a design and then manually "config" it to a desired variation but at the moment there is a problem to develop that "config". This is why I can up with the attached sketch, though I am not happy with the outcome.

I'd like to hear what you have to say. Thanks.