Namaste Nataji,
It’s wonderful that you completed the Sivananda YTT. There are many organizations that offer 1 month (or more) options. Your question is so broad, however, that it is difficult to steer you in any particular direction.
Perhaps the better question, rather than asking about intensives, is to explore the direction you wish your yoga practice to take. You started digging one well with Sivananda. Do you wish to start digging other wells? If the Sivananda teachings are relevant to you, might it be appropriate for you to go deeper in that beautiful and spiritual tradition?
Do you seek more spiritually oriented practice? yoga therapeutics? stress management training?
For deeper study, it is always wonderful to find one’s teacher, and go deep with that teacher and that teaching.
While the experiences of others can help you know what worked for them, only self-study (svadhyaya) will help you know yourself more deeply and help you determine what practices speak to your soul. Then you will know which teachers to pursue for deeper study, and the path will reveal itself.
I wish you much luck on your journey into self-discovery; the next level of training will surely emerge out of that self-inquiry.
Blessings,
Hamsa