Hey, Celeste !
Katy here from Shopify. I hope you are keeping well!
There are a couple of different ways to go about this. We have a guide on adding in related or suggested products here.
Alternatively, you may like to use an app. Some good options for this are:
Each of these apps come with a free trial period to allow you to test them out. ?
I hope this helps!
Katy | Shopify | email@example.com