So after multiple attempts of WILD I found myself sometimes just stretching my whole body, it makes me feel relaxed, it makes my body don’t feel so stiff but isn’t that also part of SP?
Should I stop stretching myself to keep that stiff feeling, cause after I stretch my body is fully flexibel again. 
SP and being uncomfortable are two different things. If you need to stretch, do so. Also remember that SP is not your ultimate goal. In WILD, you maintain your awareness as you fall into a dream. SP will happen on its own naturally, and in many cases you’ll never even be aware of it. Heck, being too aware of your body will slow down the WILD process as it’ll keep you from falling asleep.
Ah, thank you very much for replying.
After multiple failed attempts at WILD and falling asleep I got a bit to carefull and kept thinking about my body, waiting for the first effect of SP.
The thing is, after 1 month of trying I would already be happy with experiencing SP and LD would be a bonus. Well, I will relax myself and let my mind drift of a bit.
I’ve found out that if I stay still long enough my body actually gets very relaxed, to the point where I’m ready to fall asleep. The time it takes for me to achieve such state depends on how much I’m thinking about LD, SP, etc. The less I spend thinking, the faster I relax. It is in this situations where you just have to let go and wait for the opportunity of a WILD to arise.
I guess it all has to do with patience, and of course, as Rhewin said, that SP should not be your most important goal when attempting a WILD. The key here is to relax yourself to the point where it’s easy for you to see the HI in your mind. From there, the only thing left to do is to incubate that imagery long enough so that you can transition from there to the dream world, which is the problem I’m currently having. So, stretching and relaxing your body might actually be more beneficial to you than just remaining still. Relaxation is key in order to achieve a WILD.
Hope this helps. 
Well, partially the problem I’m having with WILD too is that I’m worried that I will fall asleep without me knowing it.
When I lay still for 10+ minutes than I can’t help but start extremely day-dreaming, then I think “Whoa, wait a second got to stay focused and not fall into non-lucid dream”. I can’t seem to find a balance between day-dreaming and staying focused knowing my body is laying in bed and not walking around in the day-dream.
You sound very tense while trying your WILD. First and foremost, you want to fall asleep for a WILD. If a solid stretch, and a roll over, is going to start putting you to sleep, great! Let your mind go, but try and keep just that tiny bit of consciousness there.
You will find more progress in accidentally slipping into a ND and failing, then not falling asleep at all. It will take time and practice, but you need to be falling asleep to dream.
Persistence is key!