May I sleep on my back, and without a pillow? I am a woman.
The prohibition of sleeping on one’s back does not apply to women.
Generally, there’s no need to sleep with a pillow.
However, there are health considerations too. These obviously apply to women as well.
שכיבת פרקדן – שו״ע אבן העזר סי׳ כ”ג סעי׳ ג׳.
שא״צ בכר – ראה סה״ש תשנ״ב ע׳ 141 הע׳ 72.