I have dressed and played with Dommes many times. I have been fortunate to have kinky partners and not have to go to pros, but I know one who I would gladly pay. In my experience, forced feminization can be a real turnon, especially when combined with verbal humiliation and encouragement. The SM part is optional, and as has been discussed, must be negotiated in advance. Although I enjoy bondage and moderate pain, for me the real thrill is in the psychological play. As an example, I was recently ordered to dress in a maid outfit and serve breakfast in bed to my wife and her lesbian lover. I had slept downstairs while they enjoyed themselves above me. In the course of the service, I was verbally teased by my Mistress/wife and her lover about how I looked and what a cute girl I was, but of course not a real girl, and how I could never give Mistress what she gets from a woman, etc. I was told to model different outfits while they cajoled me. The psychological affect was wonderful, a combination of praise and humiliation. I was overjoyed to be a good maid and servant to strong females.
Domme/sub play need not be all pain and suffering ... Some Dommes refer to themselves as "Loving Dommes" meaning they like to dominate in such a way that the sub is exalted and inspired to be as pleasing and lovely as possible, for the Domme's pleaure of being pampered and worshiped. The possibilities are really limitless. I think a key is knowing what turns you on and finding someone who has complimentary desires. That is what the Internet is for!