How to create fields to enter weekly sold unit for an item

How to create fields to enter weekly sold unit for an item

Hi, 

Our company has about 50 Sku, and we want to keep track of the unit sold for each sku on weekly basis.
I want to create an area where it has number fields for me to enter weekly units sold each year, what is the best way to do this?

I want to be able to use those information to also create reports comparing the same week from past years.