I found a platform in the shopify app which sells only sustainable products. They are not cheap, positioned premium but I was amazed by their products quality. I have been using them for several months and my customers loved my design with their products. I strongly recommend it. here is the website NovaTomato.com. Good luck!
I would highly recommend Blanka - Private Label Beauty, so far they are very reliable and they offer zero minimum product order quantities which is good for start up stores, also their products are high-quality, sustainable, cruelty-free.