how to find out top selling product in my niche? | warrior ... - dermaheal cosmeceuticals anti-wrinkle cream

Hi guys, I'm in the health and beauty industry, ready to sell beauty productswrinkle cream).
I haven't started an online marketing campaign yet, and I'm wondering how to do research in my segment to find the best-selling product.
I'm trying to write a compelling copy for my landing page (since I 've never done it before) so I want to get some ideas from my competitors (I won't copy of course ).
I appreciate your expert advice.