Hi Derek,
I guess the reason for the slow feedback here is probably owed to the "old school" approach of using text documents, converting them to html and uploading them by means of an ftp client.
Basically everything, except/before the upload, can be done manually with the most standard text editor. You can simply use copies of the existing pages as templates. With a little effort, try & error, you will understand what you see, do and what changes result in within an hour, maybe two.
But you won't get a folder including the pictures et.al. to simply upload like you did when you used KompoZer.
You need to upload the pictures separately, and make sure your links to them target the right folder & file. Again, if you take the time to look at one of your existing pages in a text editor, all of this is pretty much self explanatory.
You can always try to find someone local to show this to you, it's much easier than it might sound right now - and also much easier conveyed face to face - than me, not writing in my native language, trying to explain this in written.
If BlueGriffon doesn't work right now because of incompatibilities, you can try SeaMonkey, it has a composer, too - albeit much more. So it might be overloaded and confusing for what you want to do. Or you simply wait it out until BlueGriffon is updated - if it is still supported.
You can also do a search on the App Store for "html editor" or "html wysiwyg editor" and try the freebies one by one.
I fully understand that migrating the content of your current website into a website with underlying content management system seems like a lot of work and waste of time/energy - but considering the future, it's pretty much the only way to go.
You could even run both sites parallel, uploading new articles directly via CMS to the new site, keep the old site as archive and migrate its content article by article when you have some time to spare.
If the site, through its sole existence, generates a form of income for you, it might even make sense to get a quote from a professional. Set up new site, migrate content, explain the use of CMS and maybe have some form of maintenance agreement.
Maybe its even possible to find a student looking for a small web project to make some $$$. I mean the time consuming parts are the migration of content and when/where possible additionally exchanging the current pictures for the original/pictures files with higher resolution.
Again, I fully understand your intent to keep it like it is - I just thought I'd offer my thoughts on the whole situation.
Kind regards,
Oliver