The Bible says nothing about this topic. Some Christians take 1. Mose 38, 1-10 as an example, but her is a different topic. Onan interrupts the sex with his new wife (his brother died and he had to take care of the former wife of his brother and for progeny). This was against the law at this time.
But the Bible says something about sex with others and the danger to depend on something. I will come back to this topic later. Let us take a short view of self pleasure also in a wider perspective.
Hot bath, cuddle your own body, etc. are important for us and our development from the first days of our lives. We have to take care of ourself, do good things to ourself so that we are able to give something to others. At first I have to be ok and then I can give something away. That is not what God means with selfish thinking, it is a responsible bahaviour: taking care of our needs at first to build the foundation to give something to others.
You will find psychological information of the human development under this link:
https://www.simplypsychology.org/psychosexual.html
Back to the Bible:
Knowing oneself though exploring your own sexuality, the instincts are from God, checking (control) them but not letting them rule your life. In moderation like everything!
Non adultary: Drawings Fantasizing,
Pornography: dependency, not in marriage, as a standard goal is missing! It should not be the main option to get sexual satisfied.Your partner has to be responsible for this.
Do not be dependent under your sexdrives: Who is Lord of my sex drives?
Christian Help for women and men: Ask your pastor or get in contact with an organization in your country like: http://livehope.org/about-us/
