Carina, you are right. "watashi no tomodachi" is rght.
more examples:
watashi (I) + no = my and/or mine
watashitachi (we) + no = our and/or mine
e.g.,
Sore wa watashi no hon desu. - It's my book.
Sono hon wa watashino desu. - That book is mine.
boku (I as a boy or a man) + no = my and/or mine
bokutachi (we as a speaker being a boy or a man) + no = our and/or ours
anata (you) + no = your and/or yours
anatatachi (you as plural) + no = your and/or yours
kare (he) + no = his
karera (they) + no = their and/or theirs
kanojo (she) + no = her and/or hers
kanojotachi (they) + no = their and/or theirs
Carina + no = Carina's
Hanako + no = Hanako's
gakkou (school) + no = School's
sensei (teacher)+ no = teacher's
okaasan (mother) + no = mother's
e.g.,
Sore wa watashi no okaasan no kaban desu. = It's my mother's bag.