I agree with alex23. The best way to make the baby biologically yours would be to fleitrize eggs (yours or your partners) with sperm from a donor using IVF and implant the embryo in the womb of the other partner.However, this is MAJOR MEDICAL PROCEDURE and not to be done lightly. I am a medical student. It is my advice that you consult your gynaecologist or a fertlilty clinic in your area for more information. Before you go through with this, be completely sure that you are unwiliing to adopt a child. All the best to you and your girlfriend! I hope you have a lovely life and a great family together!