It's typically not the theme that converts prospects into buyers - it's the sales copy and the compelling offer.
The length of the sales page has nothing to do with the theme you've chosen. Most themes allow as much or as little narrative as the owner wants to put on the page.
Themes should be professional looking, easy to navigate, pleasing to the eye, and functional for what the owner needs to do. Beyond that, whether a theme is fancy or free, it matters not.
Good luck in your search,