✅Answer: Pay close attention to the following two narrations:

عَنْ مُحَمَّدِ بْنِ سِنَانٍ عَمَّنْ أَخْبَرَهُ عَنْ أَبِی عَبْدِ اللَّهِ قَالَ مَنْ کَانَ کَفَنُهُ مَعَهُ فِی بَیْتِهِ لَمْ یُکْتَبْ مِنَ الْغَافِلِینَ وَ کَانَ مَأْجُوراً کُلَّمَا نَظَرَ إِلَیْهِ

📚Al-Kafi vol. 3, p. 256

Translation: Imam al-Sadiq, peace be upon him, said: The one who has his shroud with him in his house is not written down among the heedless, and he is rewarded for every time he looks at it.

عَنْ مُحَمَّدِ بْنِ إِسْمَاعِیلَ بْنِ بَزِیعٍ قَالَ سَأَلْتُ أَبَا جَعْفَرٍ أَنْ یَبْعَثَ إِلَیَّ بِقَمِیصٍ مِنْ قُمُصِهِ أُعِدُّهُ لِکَفَنِی فَبَعَثَ إِلَیَّ بِهِ قَالَ فَقُلْتُ لَهُ کَیْفَ أَصْنَعُ بِهِ قَالَ انْزِعْ أَزْرَارَه

📚Tahdhib vol. 1, p. 304

Translation: Muhammad ibn Isma'il ibn Bazi' said: I asked Imam al-Jawad, peace be upon him, to order that a shirt be given to me to prepare it for my shroud, so the Imam sent it to me. I said to the Imam: What should I do with it? He said: Take off its buttons.

✅According to the narrations, a shirt that is to be used as a shroud should not have buttons.

✅There are numerous narrations on the permissibility and virtue of preparing a shroud during one's lifetime. Since, unfortunately, the ritual washing and shrouding of the deceased are mostly performed by individuals who are unaware of the narrations, and some of the narrational customs and qualities of shrouding are not observed, it is good to take action to prepare the pieces of the shroud according to the narrations. It is also good, whenever possible, to specify in one's will an individual who is knowledgeable in the narrations to perform one's ritual washing and shrouding and burial so that the sunnahs of the Ahl al-Bayt, peace be upon them, regarding washing, shrouding, and burial are observed. Insha'Allah.