Subdomain or Stand-alone Site or Sub-Folder

This isn’t a question related specifically to Webflow and SEO. However, I know there is a good scope of experienced designers and developers very active so I’m hoping for some input.

Six months or so I launched a client’s site (Wordpress) and provided SEO support. The client’s site has been very successful in rank and conversion. However, the client has really two individual aspects to his business. One aspect isn’t getting the number of inquires he would like. Unfortunately, these aspects don’t sync up under keyword searches.

So, in trying to improve SEO on the secondary aspect of the business. The client would like a new domain with highlighting a specific aspect but still including the business name. We could also use a subdomain but other than the improved URL, I’m not sure it would improve SEO that much.

I’m thinking building a second site for just the second part of the client’s business would really be the best approach.

Thoughts?