You might want to consider modified[U] siddhasana[/U]. There a host of benefits to this pose.This is generally my meditative seat/pose of choice.(Full Padmasana is advanced certainly for any length of time, and would be unwise for many people; padmasana or sirsasana does [I]not[/I] define yoga)
When doing modified siddhasana:-
[li]Don’t feel compelled to have the heel of lower foot touching perieum.No big deal.[/li][li] Also don’t expect alot of folk to have the foot of the outlying leg resting between calf and inner thigh as it is perfected.Better you have outlying leg lying in front than say force anything.You can have a cushion or block under raised knee for support. Alternate legs when tired,i.e switch.[/li][/ol]
And if neceesary you can have some leg-loosening excercises performed in dandasana ,eyes straight ahead,eyes can be closed say if you feel comfortable doing that.Can be done before-hand to warm up.
What i do when coming out or unlocking the knee safely after meditative seat, or even before, is:-
[li] Bring legs out straight,as in Dandasana…[/li][li] Then raise leg with straight arm grasping underneath lower thigh near underside knee .[/li][li] pull knee cap towards yourself by contracting the quads gently and simulataneously inhale if possible.[/li][li] Then bend knee pulling towards chest while exhaling.You can do up to 3 times each side.[/li][/ol]
This helps to safely unlock the knees when exiting or before entering a meditative seat/asana.
You can focus on rising sexual energies in the perineum (cervix for women) or root chakra and or concentrate on the third eye, with eyes closed.Feel the bliss.
*&You can do some gentle pranayam in supine position ,i.e lying down beforehand & through the nose(i believe Iyengar eventually instructed like this for certain folk like the stiff because he made the observation that many stiff folk were unable to sit and be relaxed enough,too restless or uncomfortable in the body, to bring suitable focus to pranayama so , i believe, he adopted this variation-it may not be ideal but it can be enough for v. basic pranayama for folk with such issues), to get the energies moving. This helps to relax the nervous system,calm the mind too beforehand or at any stage in practice…Bring about one-pointedness.
You can always do some light asana afterwards or before depnding on inclination and intended effect.It’s all about coaxing. If the sit bones are grounding equallythen that’s a good sign,spine upright but relaxed etc.You can continue whatever you care to do in a stable yet comfortable seat.
When you take a look at these two pics above. You can modify this seat so that the lower leg does not have to touch the perineum and the outlying leg can be resting on the floor in front.This is fine.And alternate when stiff. As long as you are stable and comfortable.Never force.At least,this is what i do.
Mukunda Stiles offers a joint freeing series -
PDF- JOINT-FREEING SERIES MUKUNDA STILES- Found affixed to this post. <SEE BELOW>
This is not the one i do but somewhat similar.For that you can check out this link here called the Pawanmuktasana series for which there are 3.
PAWANMUKTASANA SERIES-From the Bihar school of yoga and can be found in their publication [I][U]Asana,Pranayama,Mudra & Bandhas[/U].[/I] by Swami Satyananda Saraswati. Sometimes called the energy-freeing series because essentially that’s what it does.Try it out for yourself.
All these joint-lossening and energy-freeiing excercises will help you to sit in a stable yet comfortable seat.
Also janu sirsasana, you can consider incorporating that in there too.