Built a static site using Bootstrap and would like to run it through WordPress

I have built the following website using a Bootstrap blog template. I’ve styled it using my own CSS but it fundamentally keeps the same layout currently.

https://www.myhomeworkout.co.uk/

The purpose of this site is to be a blog which I add to regularly – therefore – I would like to run it through WordPress, so that I can create and add new posts and pages easily without having to create a new HTML page from scratch – all the while retaining the current css styling and layout. The problem I am facing is that I’m confused as to how I go about this. The following article shows how to import static HTML pages into WordPress using HTML Import 2 plugin:-

https://smallbusiness.chron.com/import-static-wordpress-50653.html

However I’ve also read about installing custom themes – which presumably is what my website would currently be classed as? If I installed as a custom theme then would I be able to easily add new content while retaining the look and feel of the site in it’s current state?

So really my question is what should I do next to achieve this – do I need to import the static webpages using the HTML Import 2 plug-in, or should I load as a custom theme?

I’m hosting my site through a 3rd party and will use a one-click install of WordPress.

I’m sure that there is a simple explanation but as yet I’m feeling a little overwhelmed about what I should do so any feedback would be appreciated.

Thanks
Jon