If you have never explored anal play before, visiting a well hung TS may not be a good idea. You will come off with a painful arse and regret. What I would suggest based on experience is, get a butt plug and a silicon toy shaped like a cock. Get comfortable with the butt plug easing into your anus with lube. Progress to the cock now and again use lube to go in. After a while, your arse starts receiving a cock without any pain or issue and you will start enjoying the sensations. At this point, visit a TS who is mainly top and get her to ease herself in gently. Guide her and listen to your arse, and once you are both comfortable and you are feeling good with the cock in the arse, let her go to town , if you manage to ejaculate while she is drilling you, its a sensation like no other.