Joomla: Fastest way to convert a ready html website to Joomla

I have made a couple of simple Joomla websites before. Those are using a custom template made by myself. They are easy websites as they have a simple linear menu, all pages have the same layout, just some articles are changing between pages. But in my new project, I have a ready html website that I have to convert to Joomla. The problem is, there is no one repeating menu and there is no consistent layout. To simplify a bit: there are 10 pages and they all have different layouts. Between pages background changes, menu position changes, menu content changes, content box positions change, everything changes. This means I'm not able to do this site as I've done before, using one template index.php which simply contained my repeating page structure. I am dreaming of a way to simply change ready_page1.html to ready_page1.php, adding some modules inside the php (which are then available for online editing, which is the reason switching to Joomla). I would do this to each page. The custom menus inside each page I would "manually" point to the according php files instead of the old html files. Is this method possible somehow? I couldn't figure out how to do this. I don't care loosing lots of Joomla basic functionality due to this crude method, I just want the simplest way to do this. In the end, I just want the exact same website I already have on html, but I want some chosen rectangular areas in the html pages to be editable Joomla modules. The modules would have the pen icon for editing. That's it, no other functionality is necessary.

Could you give some screenshots so you can define "different" to us of the existing layouts. It might be you can do something clever with conditional layout blocks in the template.

Based mainly on your final paragraph, have you considered using an alternative CMS, more suitable to that requirement? Something like either Perch or kirby would be quite a good fit.