Your server probably has PHP available (most do). If not, maybe ASP.
These languages are a lot more complicated than SSI, because they are more powerful. So I understand wanting to use "simpler and easier" SSI.
But, in reality, these languages actually are about the same difficulty level for simple operations.
In other words, you won't have to put in much more effort to use PHP and it will probably be better, certainly more standard. And while you're doing it you'll learn something about PHP which might help later.
For your information, here's some basic PHP code to include a page. Note that the page must end in the ".php" extension for it to work.
PHP Code:
<!--HTML GOES HERE-->
<?php include('path/to/file.html'); ?>
<!--HTML GOES HERE-->
Easy! And there are lots of tutorials out there if you need more help (or you can post here again, of course). By the way, that's how I started using PHP, when I wanted to include some other files in my page.
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