For good indoor portrait, one strobe is normally insufficient. If you are not doing this often, and your motive is indoor portrait, go and rent a studio and use all their strobes there
Not that you shouldn't own a strobe yourself, just that for the purpose of indoor portrait, you will find one strobe don't give you the results of what you need.
For proper indoor strobe, assuming you are doing high key, you will need 4 flashes and 2/4 lightbox
2 for the background paper to flood it
2 for the subject for even lightning.