Diego,
You are asking about different yoga positions (or asanas) and which ones will help you with your chakras. The truth is, they all do. It is important though that you do not focus on one or two which you feel will "help you the most" with one chakra or the other.
The thing to note about asanas is that while you can research them and find that "siddhasana will do this", or "naga-asana will do that" in respect to which chakra they focus on, each asana has one or more counter-poses that work to keep balance in the physical, as well as spiritual (chakra) development. So, they tend to go together in a form of postures, or routine. Do an internet search on "sun salutation". This is what you need to help at this stage. I highly, highly, highly recommend taking at least one yoga class with a certified instructor, at least to guide you through the asanas, so that you will know the correct posture (there are breathing techniques and other things which you will not learn from reading alone).
Ultimately it won't do you any good to perform the asanas incorrectly, and be very cautious because you can really hurt yourself if you rush into it and don't know what you are doing. But if you take the time to do it correctly, it will open up a new communication pathway into yourself and you will gain many benefits.
I am saying this because you can simply lay/sit/stand and imagine your chakras and begin to develop an understanding about them without the risk of physical harm that can occur from unguided attempts at advanced yoga techniques. Padmasana is advanced, and although it looks like you are just sitting there, there is so much more to it than that.
Embark on your journey, look around, breathe in the air. By the time you get to your destination, it will be the events that you have gone through which will have given you the wisdom to understand where you are... otherwise you will just be sitting there with your legs crossed and a pain in your knees.
Namaste
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