There is nothing like that mentioned in any Hadith that you cannot recite the same surah or that the Surah in present Rakat should be greater than the next Rakat surat. In fact, Surah Fatiha is the only thing you are required to recite. You do not have to recite anything else, although it is mustahab to do so.
It was narrated that ‘Ata’ said: Abu Hurayrah said: In every prayer there is recitation. What we heard the Prophet (peace and blessings of Allaah be upon him) say, we tell you, and what he did not tell us about we cannot tell you. Whoever recites Umm al-Kitaab (i.e., Soorat al-Faatihah) has done enough, and whoever does more than that, that is better.
-Narrated by al-Bukhaari, 738; Muslim, 396.
Recite whatever is easy for you. Allah has made Islam very easy for us.
So recite what is easy from it [Quran]