Salah of an elderly or sick person who cannot stand up

Q: I usually perform one or two Rak`ahs (units Prayer) from the obligatory Salah (Prayer) standing and then complete the Salah sitting. Is it permissible for me to do this or not as I am now 65 years old? Please advise me of what is correct.

(Part No. 8; Page No. 70)  A: If you are unable to complete the Salah standing or you suffer a lot when doing so, you may complete your Salah sitting with no problem and your Salah will be valid. However, if you are able to complete the Salah standing with no great suffering, and yet you complete it sitting, just to make it easy for yourself or because you want to rest, your Salah is invalid. It is authentically reported that the Prophet (peace be upon him) said to `Imran ibn Al-Husayn (may Allah be pleased with) when he was ill, "Perform Salah standing, and if you can not, (perform it) sitting, and if you can not, (perform it) lying on your side." (Related by Ahmad, Al-Bukhari, and As-hab-ul-Sunan [authors of Hadith compilations classified by jurisprudential themes]) Al-Nasa'y added - with a Sahih (authentic) Sanad (chain of narrators), "If you can not do that, (perform it) lying on your back." If someone offers Salah while lying on their back, their feet should be in the direction of the Qiblah (Ka`bah-direction faced in Prayer). May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.