Question

Hello and blessings!
The words of the Magen Avraham, section 239, subparagraph 2:
“…And in truth the psalms are not an obligation at all; only Shema and the blessing ‘Who casts the bonds of sleep’ are obligatory. Rather, the custom developed to say them because we see that Rabbi Yehoshua ben Levi said them. The custom is to say them, although even Rabbi Yehoshua ben Levi said only the two psalms. The practical difference is regarding a sick person or someone under compulsion. And the fact that women did not adopt the custom of saying it may be because they hold that since it applies only at night they are exempt, for it is a time-bound positive commandment, just as they are exempt from reciting Shema.”
According to this Magen Avraham, the obligation is only the blessing “Who casts the bonds of sleep” and Shema.
There is no reason to abolish a custom so long as its rationale has not lapsed (Magen Avraham, section 691, subparagraph 22), but here, where the point is protection from harmful forces, I wondered: would it be possible not to say anything besides Shema and the blessing “Who casts the bonds of sleep”? That is, of course, assuming that Shema and the blessing are not only about protection, but also because we derive it from the verse, “Speak in your hearts,” as written in Berakhot 4b.
Also, in the middle of writing these lines, I saw that Maimonides omits the matter of the psalms:
Maimonides, Laws of Prayer and the Priestly Blessing 7

Halakha 1
When the Sages instituted these prayers, they also instituted other blessings to be recited every day, and these are they:
When a person goes to bed to sleep at night, he recites:
“Blessed are You, Lord our God, King of the universe, who casts the bonds of sleep upon my eyes, and brings slumber upon my eyelids, and gives light to the pupil of the eye. May it be Your will, Lord my God, that You save me from the evil inclination and from harmful occurrences, and do not terrify me with bad dreams or evil thoughts, and may my bed be whole before You, and raise me from it to life and peace, and enlighten my eyes lest I sleep the sleep of death. Blessed are You, Lord, who gives light to the whole world in His glory.”
Halakha 2
He then recites the first passage of Shema and goes to sleep, even if his wife is sleeping with him (he recites the first verse or verses of mercy, and then sleeps).
And if sleep overcomes him, he recites even the first verse or verses of mercy, and then sleeps.
Thank you!