بسم الله الرحمن الرحيم
The way in which you offer salah sajdah is not done properly rather it is done with gesture. So instead, if you sit on ground whether by sitting upon your hams or by stretching the legs and offer salah by gesture then it is better for you. You should do it in fardh salah at least.
(2) When you have no problem in offering salah in the mosque, then leaving the salah in the mosque with jama’ah completely is deprivation from big reward. You should arrange some chair etc for it.
(3) In case you cannot sit on ground in any way and you cannot arrange chair then it is lawful for you to offer salah at home. But in case your excuse is not feasible you shall not get the reward of performing salah with jama’ah.
Allah knows Best!
Darul Uloom Deoband