Fertility drugs. Your best option would be fertility drugs like clomid.
You won't get them unless you've been trying for at least a year and you need them. But they would be your best option.
Or you could try invitro. They could implant you with more than one and you could hope they take. I think they can also give you the sex you want that way too. Some selective something or other.
Both these options take time and money - and you will only be able to do them if they are necessary. No doctor will just do them without reason.
Your grandma won't care whether it is twins or not. She'll just be happy for a baby.