Hank here from Shopify. Really great question!
There are a couple of ways you can add the related product feature to your store, I will list the different options for you to take a look at below. However, the specific feature you are looking for may require coding.
The first option would be through the use of a third-party app. I have found three apps for you to take a look at, to see which one would be most suitable for your store.
Then the second option would be through the theme code itself. I have a guide that goes through how to do this here, but this tutorial would not be supported by Shopify.
Hopefully, someone with more technical skills in the community will come across this and be able to add some value to you here, but if not, your best bet might be to reach out to one of our Shopify Experts should you need further assistance with this.
I hope this helps, Hank.
I just released an app that allows you to have two cross-sell sections as you've described. It's automatically configured for free themes but easily configurable for custom themes. Please let me know if you have any questions or concerns or require any assistance: