Service page and Pillar page keywords problem

I want to implement a Topic cluster in my local service business. But here's a small problem I can't figure out. Any suggestions are most welcome.

Business service and all of the content are local and for local. So keywords monthly searches and competitions are low. But that's okay.

I have a service: Graphic Design

So, normally my graphic design service page keyword is: graphic design. ( have a small number of monthly searches. But this is the highest)

Now I have to create a pillar page. Right? If so, others keywords related to 'graphic design' are a too low number. All of the articles, videos about the pillar page say, I have to choose a keyword that has a big monthly search and a small. And choose a long tail keyword for the sub topic.

But, already I choose the 'graphic design' keyword for my service page. For the pillar page, I have nothing much. And for the sub-topic, nothing.

In this scenario, what will be my best strategy for the Topic cluster?