Customer Flow when they purchase specific product

Hi Everyone! 

Klaviyo user for a number of years now, however I’m unsure how to approach this specific use case. 
I’m going to be listing products that are fulfilled via my printing partner in my store, so I’m looking to create a flow so these customers get a different post purchase email sequence. These products will be in their own collection (shopify)

I’m thinking i’ll need three flows in total
1. Customer orders just the printed product
2. Customer orders printed products plus other products that I fulfil
3. Customer doesnt order printed product (this I already have setup)

Where I’m getting a bit stuck with this is the logic around the triggers to keep things tidy & easy to maintain so just looking to get some guidance. 

I could either create a specific list for users who buy the printed product and then a flow for those?
Or create three triggers based on the purchase behaviour (above) which i add into my current post purchase thank you sequence & just add the different flows there? 🤔

Would love to hear your thoughts & help!
Thanks!