If still you are looking for a solution to offer something post purchase,
You can check with this app : https://apps.shopify.com/wizio-post-purchase-upsell
Looks perfect for your requirement.
This article, How to Customize Shopify Thank You Page and Make It Shine might be helpful to you. As it mentions, there are many apps can help you build your Thank You page, such as:
However, having a perfect Thank You page is part of having a great post-purchase experience. Consider what your customers care about after the buy button, yes, where their orders are. Compared with a thank you page builder, an order tracking solution allows you to do more things, including:
If you're interested in exploring the best order tracking solutions, you may try ParcelPanel first, which is trusted by over 300,000 Shopify merchants, and rated 5 out of 5 based on over 1,300 reviews.
Click the link here to get a 30-day free trial