I'm for an app that when someone adds an item to the cart there a sidebar that show the current cart+ best sellers.
If you're looking for an app that allows you to display recommended products after clicking the add to cart button. I suggest checking PickyStory's bundle popup widgets. You can create bundles and set them as a popup that will show if a customer buys a product from your bundle.
The popup widget looks like this:
You can also check our live demo here: https://try.pickystory.com/products/orange-t-shirt
You can display the popup widget on your product page or on your cart page.
How are you?
I would like you to try our iCart Upsell & Cross-sell app (with 60 Days Free Trial - BFCM offer) that's perfect to satisfy your requirement.
There are more amazing things in it I would suggest you check...!!!