What will be best to do in this situation?

My step-son (12yrs) wants to come and live with us for a year or 2. It is OK with the mother. The only problem is that she doesn't want to go to court to change the court papers ( child support & visitation) We all live in Texas only 14 hrs apart. She said that she will signed two different notarized letters.One approving the child to come & live with us and the other where she will be returning what my hubby sends her as child support. I honestly think it will not be totally legal and in a future if there is a problem in the future it will not be legally validated. I asked a lawyer ( by phone) and he told me he will charge around $1500 to fix everything from where we live but if for any reason she doesn't agree with anything my hubby will have to travel to her hometown and fix everything there. Now we don't know what to do and what will be best to do or if a lawyer can make like a letter agreement between them and be more validated than a notarized letter. Any advices on what to do or what will be best? Thanks in advance :)