It is actually not absolutely necessary to have a spiritual father or mother in order to practice the Jesus Prayer. St. Ignatius Brianchinanov (spelling?) in his wonderful little work on the Jesus Prayer mentions that, due to a lack of good spiritual guides in his day, one may "replace" a spiritual guide with extensive spiritual reading. I'd recommend checking out the great Russian Fathers, particularly the above mentioned Ignatius, as well as St. Theophan the Reclude and St. Seraphim of Sarov.
Roman Catholics may most certainly practice the Jesus Prayer according to their own traditions since devotion to the Holy Name is not something limited to the East or Orient.
The key is focusing one's attention on the prayer with "the mind in the heart" as St. Theophan said. This is very difficult for some, very easy for others. For some prayer with the mind in the heart comes quickly, for others it takes years, and for others still they never quite get there despite intense struggle. Ultimately it is a gift.
As to postures, breathing techniques and other physical aids, the Fathers are universal in discouraging this unless one has an experienced guide. Sts. Ignatius and Theophan seemed particularly against this tradition altogether. Again, the main thing is prayer with the mind in the heart. This is the main reason I do NOT recommend the Way of the Pilgrim. The author of the book focuses quite a bit on the breathing techniques and other physical/mental techniques. These things can be, and in fact are quite dangerous if one doesn't have an experienced guide.
If you can, find a copy of "The Art of Prayer: An Orthodox Anthology". It is a wonderful little book consisting of quotes from a good number of Fathers, but mostly from St. Theophan. It is the best introduction to the Jesus Prayer and Eastern Spirituality that you will find anywhere.
And if you would like a prayer rope, I make and sell them. Just send me an e-mail at firstname.lastname@example.org
ICXC + NIKA,