In the Catholic tradition we have great mystics such as St. Theresa of Jesus, St. John of the Cross, etc. And they achieved altered states of consciousness by praying the rosary, which is nothing more than repeating the same prayers over and over again. That is transcendental meditation.

Another way to do it is to choose a phrase or a sound (I use "Sat nam" or "Om mani padme hum") and repeat it in your mind for 20 minutes in the morning and 20 minutes at night.

For the posture use the posture that Zen monks use when they do Shikantaza. Search for "zen meditation posture tutorial" on youtube and it will come up.

It's not a fancy course, but it will work for you.