Lightweight theme builder plugin to use with a custom theme built with ACF PRO

My client has a large woocommerce site built with a custom theme using ACF Pro. He wants to add a lightweight theme builder to easily create new landing pages.

So we can't switch the theme to something like Divi. We need some plugin that works like a builder like Elementor. But Elementor gets heavy so I am wondering if there is any theme builder plugins that's light weight and gets the job done. We won't need to modify or change header and footer but just want to build the body.

Thanks

PS. Gutenberg is disable. It has classic editor.