I have sometimes thought of this for myself as well, but then thinking realistically, I know I couldn’t handle it at this point. And you have to especially take into consideration your own children’s feelings and concerns. Remember you would probably have to deal with behavioral stuff while the child is adjusting. And definitely have to deal with any specific problems that child has.
You may want to inquire into it through an agency like Ohel to see what the practical ramifications might be. Once you have educated yourself and your husband, then you can make an informed decision.
If you do decide to take in a foster child, then Yasher Koach and Tizku L’mitzvos!