The tag you added is for Yoga-Asana. But your question seems to be about seats.
I am answering for both.
Manufactured seats, like those made of wool, Kusha etc, are needed.
Seats made of wool, blanket etc are good to use. On the other hand, seats made of wood etc should be abandoned.
VamshAshmadharanidArutrinapallavanirmitam | ...
Gheranda Samhita is another text which describes Asanas and Mudras in details. Along with Hatha Yoga Pradipika and Shiva Samhita, it is one the 3 classic treatises on Yoga.
The performance of Asanas is done in order to gain Dhrirata or firmness.
So, Asanas, Mudras etc are practiced as part of a larger Yogic procedure.
The 2nd Chapter of this ...
Yes , The practice and perfection of Asana is a prerequisite for pranayama. The Yogic scriptures tells us that that we should practice pranayama after fully acquiring technique of Yoga Asanas i.e. postures.
If our internal organs are not healthy, not strong and balanced, then the practice of pranayama will have an negative effect on our body and mind....
Vajroli mudra is quite an intricate Yogic practice,It involves sexual intercourse too.
So,I don't really understand why you want to know about it from online resources.Or are you looking for some other Vajroli that i don't know about?
In anycase, in Hatha Yoga Pradipika,we find the following description of Dasa mudras including the Vajroli mudra:
As per the Samvarta Smriti, Achamana , if done while sitting on a seat or while sitting on one's thighs,the act does not purify the performer.
That is possibly the reason why squatting is considered as the recommended posture for performing Achamana.
A S'udra becomes purified [by touching the twelve limbs] with his hand
; a Vais'ya, with water '...
Yes apart from Hatha Yoga Pradipika a text called The Yoga Yajnavalkya is describing these asanas. Yoga Yajnavalkya is a dialog between well known Rishi Yajnavalkya and Gargi a Brahmavadini.
Chapter three of Yoga Yajnavalkya is describing list of eight asanas in detail with procedure. These Asanas are Svastikasana , Gomukhasana , Padmasana , ...
It is not recommended that you meditate while lying down. One has to sit at least in an upright position.
Quoting from the book "Meditation and its Practice" by Swami Rama.
Suggestions for Making Sitting Positions More Comfortable:
It is not recommended that you meditate while lying down. There are several reasons for this. One of the most important ...