Grown child coming into my/our life

Please no negative comments. I really want this to be a positive change for all parties involved. My SO has a child. His child's mother got in touch because the child wants to get to know my SO. I want everything to go smoothly. I want to be supportive to my SO. Also this will be a big change in my life, how can I make the child feel comfortable etc? Anyone out there have any advice? Anyone out there who can give advice as what would be best for the child? All I know is I will not make the child call me "Mom" or anything like that, the child can call me whatever they feel comfortable with. Thanks for advice