Hi, I am in a similar situation to yourself. I have paid for a consultation with a lawyer previously. Unfortunately the advice I received was along the lines of “it doesn’t matter if the father is not involved with your son at all or doesn’t pay maintenance, if you don’t get his written permission, it will be highly unlikely you will be able to change your sons surname. The courts do not like doing this”
Even if the father was a criminal it sounds like there is little chance of courts agreeing to it. The only chance you may have is if your son is old enough and can express his own will to the courts (old enough as in teenage age or approaching I would guess)
It totally sucks. But what you can do is use a “preferred name” for him. I have done this at school so my son uses my maiden name there and there is no issue. But for prescriptions etc, flights, you will have to use the legal name.
