1, Folding arms while praying was never practiced nor permitted by the Prophet Muhammad (SAWA). It was started by Omar Ibn al-Khattab when he saw the Zoroastrian prisoners of war who were brought from Persia to Madina folding their arms as a sign of respect. He ordered people to do that during Salah. Leading Sunni scholars like Ibn Rushd in Bidayat al-Mujtahid page 323 admitted that there is no evidence at all that the Prophet (SAWA) ever folded his hands or arms during praying.
Sunni well know scholar Malik ibn Anas who is the founder of Maliki Sunni sect refused this practice of folding hands while praying.
'Many well known Sahaba (Companions) refused folding hands like Ibn Abbas, Ibn Mas'ood, and above all and most importantly Imam Ali (AS) who was ordering Muslims to do this practice which is from non Muslims.
2.Sajdagah: We follow the real Sunnah of the Prophet Muhammad (SAWA) who never prostrated during prayers on carpet or textile and used to put his forehead on the earth. He said: The earth was made for me as place for prostration and purification. جُعِلت لى الأرض مسجدا وطهورا
That is why we put Sajdagah to put our forehead on the clay of the earth like the practice of the Prophet (SAWA).