Selecting Product for E-commerce

I want a way to find products that are not feasible to sell in physical stores due low demand. After that analysing going after these niches with e-commerce sales channels. A sweet spot got to be found where the demand is not too high for the product to be placed on stores shelfs yet high enough to be sold online. I wish to build a process to find, analyze, experiment, sell, and eventually stop selling to overall optimize reward-effort ratio.