An app that offers advanced product options is going to accomplish what you need in terms of having drop-downs on your product page that your customers can select to add-on to the base product at additional costs/free. Below are a few great options:
All these apps offer free trials that you can use to test the functionality of the app. From there, you can choose one of their paid plans to continue.
As far as a cross-sell pop-up app, this would require a second app as it’s a completely different set of features. There isn’t a combination app to my knowledge that does product options + upsell pop-ups. There are a wide variety of upselling apps here. An app called Upsell Bundle Discounted by Ultrasale is a good option I’d recommend looking into.
What type of products do you sell and do you have specific add-on features that you are looking to sell/showcase to your customers?
If there is anything else I can help you with, please let me know.