You might not like my suggestion, but it is to learn html. In the many years since starting with Frontpage, surely you have noticed a few drawbacks. There are templates (some free) that will give you one site for all users and save the headaches of trying to set up and maintain two sites. The templates let you work in a plain text editor, view your progress in your browser, on your computer and upload to your site when you like the results. A few weeks (or less) spent learning the basics of html and getting a handle on css is the most liberating thing a webmaster could do.
The 2 site approach is the least favored way to have a mobile friendly site because of the myriad of devices, screen sizes and resolutions to be identified and redirected to the right version of css to deliver their format. You are not likely to find a WYSIWYG editor for mobile that can deliver a good user experience on a separate site.
See this issue discussed today: [webmasterworld.com
...] that shows what happens when people find your site in search and get automatically sent to your separate mobile site. The reasons not to build a separate site for mobile are a long list of new problems that you don't have right now.
If creating a mobile app is too complicated, I don't think you'll find an equivalent to Frontpage to build a mobile site, nor do I think that separate sites is the best path to choose.
I hope someone pops in with an answer that you will like better that can do just what you want, but this is my suggestion.