Should I start a new site or do it on my already existing site?

I have basically made a one-product store and optimized the store and it just recently started ranking very well. I think this is due to topical authority which I have focused a lot on.

Now I want to rank another product and I wonder if I should create a new site or if I should try to rank it on my existing site.

both the products are in the same niche but the niche is very broad.

thankful for answers!