Cudy

Before installing it, I was worried due to its ratings in the reviews. However, it turns out to be a good Shopify Form App with comprehensive features. You can create different types of fields, rearrange them, and post them, in styles you like—Pop-up / Inline / or a Single landing page. New fields will be connected to customers' metafields. Responders' answers will be filled in, so it's quite easy to handle the data. I just created one page, and I think that's the form app I need.