Hi Fabio. I had a similar challenge as you and also needed about 40m with spot dripping. After years of trying and discarding material: the pressure reducers from Gardena are toys. The pressure reducer in this set is for nothing and the big one from Gardena burst on me 2x.
I have installed a professional pressure reducer (like a house connection) in the garden and can connect it with a hose. Behind this I distribute the water to 3 strands. I run two of these lines with pipes, distributors and drippers from this Gardena system. That works ;-)

15 m main pipe 10 m branch pipe for dripper; see pictures.