Good luck, i tried a T shirt business online years ago. Created a store on shopify.
The problem is the market is saturated and advertising costs way too much, the suppliers charge too much and therefore margins were too low. It cost me about £7 in advertising revenue to sell a T shirt i made £5 on.
You will find similar, I've seen online videos talking about how to setup a store doing online supplements already, I'm assuming you must have seen similar, and so will tens of millions of others.
Good luck, not saying don't do it, but be prepared this will not be the passive income boost you think it will be. Especially if you arn't familiar with it. The ship has long sailed once you see people talking about it on social media.
I see you've already said you've got small margins, you need to really stop and think about the advertising costs as well, if they are not already factored in you are facing an uphill battle.