The bible isn't really a list of do's and don't's. Even the Law isn't really a Law the way we think of laws today. In our legal tradition, you have this large framework of principles, and then you have a ton of specific laws that cover specific things, and if there isn't a law about something its not illegal. The systems of law in the ancient near east were different, and the Torah is like them. They're casuistic - they're like a series of case studies or principles from which you should reason the legal or moral imperative for whatever situation. It's more like what the supreme court does, less like criminal court.
So, I think looking to the bible for an answer in black and white to something like your question is not going to be helpful.
In my own opinion, I'd put this under "All things are lawful but not all things are profitable; All things are lawful, but not all edify. Let no one seek the good of himself, but that of the other." What is profitable for one person is not for someone else. What is edifying for one person may be harmful for the other. And no one can truly judge that but the people in the marriage, or perhaps those who they have some kind of very intimate advisory relationship with - like a close friend or parent, or something.
To really know whether these things are right or wrong would probably need the people involved to really inquire of themselves - why do I want to do this? Maybe 5 whys to really find out. Maybe the answer is good. Maybe it is not.
So, I think looking to the bible for an answer in black and white to something like your question is not going to be helpful.
In my own opinion, I'd put this under "All things are lawful but not all things are profitable; All things are lawful, but not all edify. Let no one seek the good of himself, but that of the other." What is profitable for one person is not for someone else. What is edifying for one person may be harmful for the other. And no one can truly judge that but the people in the marriage, or perhaps those who they have some kind of very intimate advisory relationship with - like a close friend or parent, or something.
To really know whether these things are right or wrong would probably need the people involved to really inquire of themselves - why do I want to do this? Maybe 5 whys to really find out. Maybe the answer is good. Maybe it is not.