Yes Jannah is under the feet of our mother. After Allah and our Messenger....the most important person is our mother.
This one isn’t a direct quote the Prophetﷺ but of his close companion and friend Abdullah ibn mas’ud (May Allah by pleased with him)
Zirr ibn Hubaysh reported: A man came to Ibn Mas’ud, may Allah be pleased with him, and he said, “O Abu Abdur Rahman, which degree of Islam is best?” Ibn Mas’ud said, “Prayer.” The man said, “Then what?” Ibn Mas’ud said, “Charity.” The man said, “Then what?” Ibn Mas’ud said, “Righteousness to parents.”
Source: al-Mu’jam al-Kabīr 9824
Grade: Hasan (fair) according to Al-Albani
عَنْ زِرِّ بْنِ حُبَيْشٍ قَالَ جَاءَ رَجُلٌ إلى ابْن مَسْعُودٍ رضي الله عنه فَقَالَ يَا أَبَا عَبْدِ الرَّحْمَنِ أَيُّ دَرَجَاتِ الْإِسْلَامِ أَفْضَلُ قَالَ الصَّلَاةُ قَالَ ثُمَّ أَيٌّ قَالَ الزَّكَاةُ قَالَ ثُمَّ أَيٌّ قَالَ بِرُّ الْوَالِدَيْنِ
9824 المعجم الأوسط للطبراني
753 المحدث الألباني خلاصة حكم المحدث حسن في صحيح الترغيب