His wife cannot conceive now and he wants more children

About xxx years ago my wife underwent a hysterectomy to remove her reproductive organs.  She took this step by herself, under doctor's consent, because of complications with her ovaries and scarring.  I wanted to have more children with her, and now that we are Muslim, I want them even more in order to bring them up in the deen of Islam. I felt a deep sense of regret when she had her operation, but was hesitant to say anything because I did not want to worry her.  Later, after the operation, she changed.  She had many complications, and lost interest in me sexually. I still want more children, and I am getting older.  We have two -- one together, who is xxx, and a stepson, who is xxx.  The younger one has received Islamic instruction and accepts Islam as his religion, but the older one rejects it completely.  I love them all, but the situation saddens me.  I would like to start a new family, not discarding old one.  She prohibits me from another wife (but not in the contract), and I know she will leave me if I do.  My question is, what advice do you have to give me?  I love my wife, but I want to have more children, and my desire to be a father once again, raising my children in Islam is strong.  She also rejects adoption, even if it were halal. I am just looking for a way out of my dilemma.  Do you think my desire to start another family is halal? What does Islam suggest in this case?