I’m not sure I understood you correctly. Are you saying you actually want to go with him when he has sex with Trans prostitutes? That’s a new one on me. I’ve heard of sitting in and watching, maybe someone known?, but not to go to a prostitute with a man/woman. I truly don’t think that’s a good idea. I couldn’t handle watching it myself.
If you’re trying to help things, perhaps start with a therapist. Most start with individual therapists, and then after they get a good footing, go to a marriage counselor together.
Or, talking to each other, getting books on the subject and looking online to educate yourselves and talk to each other.....talking is good.
But, if he isn’t willing to stop, it’s going to be up to you as to how to proceed.
If you’re wanting to add things to your sex life, maybe add them to your bedroom. Sex toys are good. Some couples go to the ‘toy store’ together and that puts some fun in it and can take the scariness and seriousness out.
The one thing I wouldn’t do is go with him to a prostitute.
Good luck with whatever you both decide.