The Blessed Mother specifically asked that the Miraculous Medal be worn around the neck. I use dental floss for mine as it’s very strong and easy to replace when it wears out - we always have dental floss in the house. Just be sure to tie really good knots in the floss.
I suppose if there’s some reason you really could not wear it around the neck you could put it in your wallet.
St. Benedict is also a good saint to call upon and to use his medal, but you specifically mentioned asking for the Blessed Mother’s help, so it seems you would want to use the medal of her.