Hi @ajohns ,

Thanks for your question and great to hear you’re working on a post-purchase flow! 

There is actually something that works as an If/Else condition for templates and designing your emails! Inside Klaviyo, this is referred to as a dynamic variable. Dynamic variables can be utilized in templates as you can show or hide things based on variables such as if someone has bought a product. 

The first thing you'll want to do is make sure to set up Product Feeds so that you can pull producst from certain categories/collections: How to Use Product Feeds and Recommendations. Under your Data Feeds tab, you can set up Product Feeds to include only items from specific categories, which you can then use to populate products in your Product Block.
Once you've made your feeds, you can include them in your email content and use Show/Hide conditions to only display them when particular conditions are met: How to Show or Hide Template Blocks Based on Dynamic Variables. Since you're wanting to display these blocks based on a person's purchases, you'd likely want to include this in a Flow that is triggered by an event (Metric-Triggered Flow).

Hope this helped and feel free to report back with updates!

Alex