Do you have a Mix&Match option where customers can build their own bundle?

Yes, we have a functionality which allows your customers to build their own bundle based on the requirements which you set up. 
To create such bundle, select all products on which you want to offer the discount and set the discount for these products. Then configure the discount condition to Buy minimum/maximum number of items from the bundle and set the minimum and maximum limits. 
Also make sure to check the box which allows you to use the Mix&Match display for this bundle. 

Make sure that you also set up the maximum allowed quantity of each product to more than 1, so your customers can buy more than just 1 item of every product. 

You can read more about discount conditions here.