2.46 The posture should be steady and comfortable.
2.47 In effortless relaxation, dwell mentally on the Endless with utter attention.
Steadiness of body and mind go hand and hand like milk and Oreos. In my practice of meditation I have noticed that muscle tension is a reflection of mental tension. For instance, I sit most of the day at work and I get these really annoying tense muscles in my ribs. I forgot the exact name, but it's in the left side just below my pecks. This was something that had been bothering me since I was about the age of sixteen. When I started doing things such as progressive relaxation and breathing, I learned how to take conscious control of the muscles and let them relax.
The thing is, the pain will always come back during times of stress. IT support is not what I would call a relaxation profession and I am sure anyone who sits all day in a high pressure environment will experience some sort of discomfort. Once awareness of the tension is realized, it tends to hurt more. It's not that it's actually hurting more, you are just noticing it instead of mentally blocking it out. Our minds are amazing the way they adapt, aren't they?
Traditionally, Yogic meditation is practiced sitting down with the spine perpendicular to the floor. Metaphysically speaking, this is so prana can flow through the spine without hindrance. Practically speaking, you will fall over if you start to fall asleep. Falling asleep is not a bad thing, it shows that you are getting to a level where your mind has been calmed. When the mind is calmed, it's natural instinct is to fall asleep. Meditation is the line between awake and asleep.
So what posture should you use? You should do whatever makes you feel comfortable. If you can do the lotus position, more power to you, but if you have to put more effort into holding a position, then doing meditation, it will just interfere. I used to fret over what kind of position I should use, but after a decade, I just plop my ass on the couch and sit cross legged. Since I am not Gumby, I don't foresee myself ever being that bendy.