You cannot design products to retail like this. That is the problem. The design must be sold to everyone to make it competitively viable at large scale for contract manufacturing. Making many sizes is something that is untenable and will fail as a commercial venture. It causes overburden and poor turnover rates in the supply distribution and retail chains. The product does not have sufficient margins to support this type of system. The competition that already exists has set the price expectations. No one will pay the required pricing needed to support this business model. You would be paying 2-3 times as much per unit in order for retailers and distributors to justify the enormous investment and management of the overburden risk.