7 – Buy two, or more exact same products and get a better price discount

I want to create a promotion like “2 for 27,90$, 3 for 39,90$”.

I have installed the discount_extra module and rules too, so I can solve with the “Order discount -> Per-quantity product discount (% off)” for a specified product if I add the SKU to trigger the discount, but with this solution, I must create too much discount for every product.

I want to create a “global rule”, so if the discount is active that’s triggering if the consumer buys more of the same product.
I’ve tried to solve with rules and commerce:line-item but without success.

Any idea how can I solve it?