Always, the way forward is with a minimal test. It will always be overwhelming to think about converting what you have to ... anything! That is how most projects turn into a mess, because the developer is too intimidated by the size of the task involved in upgrading.

To solve this, start small. In the case of converting a site where all the HTML is hard-coded in the Perl, and you are considering moving to a Template system, this means: do not consider trying to accomplish all the job! Consider instead taking the first step.

• Install TT2, and in a completely separate project, write a 10-line Perl script that uses a 10-line template to output an HTML page. Make sure the Perl script uses no HTML and no hard-coded text that will be in the output.
• This will take you ~ 30 minutes. After, enjoy the feeling of awesomeness you get from separating your HTML from your Perl. Have a cup of tea, then go back to your regular work. Even if this means going temporarily down the "wrong" path.
• Next day, or next chance you get, go back to your new stuff and make the template pull in ("Process") another 10-line template. Put some condition in the Process directive in your main template so the sub-template is "chosen" in some way. (Like you might do with languages).
• This will take you ~ 30 minutes. After, enjoy the feeling of awesomeness you get as you realize that structurally, you are now halfway to your goal. Have a cup of tea, then go back to your regular work. Be prepared to feel impatient with your regular work, and to stay late after getting it done, to work on your new project.

And so on. Within less time that you imagine it will take, you will be on your way to an upgrade. But you have to take the first step . . . in the right direction.