UoM conversion factor

I started using this program a couple of days back and absolutely love it.

I'm having a bit of a problem here. I tried searching for it the forum and came up with nothing. At least in this section anyway.

I'm looking for a way to convert between UoMs. The "Purchase Pricing" works only when the supplier and the company use different UoMs. And the unit once set for a product cannot be changed will placing a purchase or sales order. The problem is we use 2 types of units for the same product. For example, we sell in dozens but sometimes end up selling in pieces as well. Is there any way in which the 2 units can be connected, like 12 pieces = 1 dozen and have the option to select the unit while placing an order?

sun