All Praise to Allah Subhanahu wa Taala and blessings of Him be on Prophet Muhammad peace be upon him His family and companions
See these ahadith which would In Sha Allah clarify your doubt ,
قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " أَكْثِرُوا الصَّلاَةَ
عَلَىَّ يَوْمَ الْجُمُعَةِ فَإِنَّهُ مَشْهُودٌ تَشْهَدُهُ
الْمَلاَئِكَةُ وَإِنَّ أَحَدًا لَنْ يُصَلِّيَ عَلَىَّ إِلاَّ عُرِضَتْ
عَلَىَّ صَلاَتُهُ حَتَّى يَفْرُغَ مِنْهَا " . قَالَ قُلْتُ
وَبَعْدَ الْمَوْتِ قَالَ " وَبَعْدَ الْمَوْتِ إِنَّ اللَّهَ حَرَّمَ
عَلَى الأَرْضِ أَنْ تَأْكُلَ أَجْسَادَ الأَنْبِيَاءِ " . فَنَبِيُّ
اللَّهِ حَىٌّ يُرْزَقُ .
It was narrated from Abu Darda’ that the
Messenger of Allah (ﷺ) said: “Send a great deal of blessing upon me on
Fridays, for it is witnessed by the angels. No one sends blessing upon
me but his blessing will be presented to me, until he finishes them.”
A man said: “Even after death?” He said: “Even after death, for Allah
has forbidden the earth to consume the bodies of the Prophets, so the
Prophet of Allah is alive and receives provision.’”(Ibn majah)
and
Dawud said Marwan [ibn al-Hakam] One day saw a man placing his face on
top of the grave of the Prophet.He said: "Do you know what you are
doing?" When he came near him, He realized it was Abu Ayyub
Al-Ansari.Then he said: "Yes; I came to the Prophet, not to a
stone.(Ahmad,Tabarni,Ibn Hibban,Al Hakim,Ibn Tayyimia in al-muntaqa)
Ahlus Sunnah wal Jamah believe that Prophets are alive in their graves as mentioned in hadith similarly Allah Swt has said about Martyrs that they are alive and dont consider them dead.
And do not say about those who are killed in the way of Allah , "They are dead." Rather, they are alive, but you perceive [it] not.(Quran 2:154)
So Martyrs are not above the level of Prophets so when they are alive how come we could not assume such about Prophets as well by the above clear hadith.
Imam Ibn Hajar alAsqalani (Ra) said in Sharh of Sahi Bukhari "fath ul Bari"
واحسن من هذا الجواب ان يقال ان حياته صلى الله عليه وسلم في القبر لايعقبها موت بل يستمر حيا والأنبياء احياء في قبورهم
The best answer in this context is that Prophet (Peace be upon him) is alive in his grave and death will never reach him , but he will remain alive due to this fact that the Prophets remain alive in their graves.
Now see this please for more clarification,
Anas reported Allah's Messenger (ﷺ) as saying: I happened to pass by
Moses as he was busy in saying prayer in his grave, and in the hadith
transmitted on the authority of 'Isa there is an addition of these
words:, I happened to pass on the occasion of the Night
journey."(Muslim)
It was narrated from Anas that: The Prophet (ﷺ) said: "I passed by the
grave of Musa, peace be upon him, and he was praying in his
grave."(Nasai)
Now as you stated about God like attribute "to consider alive as shirk" so regarding this when we consider someone to be alive it is not "Shirk" as we are alive yet but it could be if someone claims that He is alive from the beginning and he was not created later and this is called as HAADITH(Something which was not before but created later) so Allah Swt is from beginning but no body else is like that.
So everyone and Everything is "haadith" except Allah Swt and His Attributes.
Shirk Fis Sifaat is something when you consider these attributes of Allah Swt for someone else:
1- All attributes of Allah Swt are from beginning (Azali)
2- All attributes of Allah Swt are forever.(Abadi)*
3- Every Attribute of Allah Swt is infinite.(La mahdood)
4- All Attributes of Allah Swt are immortal.(Ghair mumkin ul Fana)
5- All Attributes of Allah Swt belong to himself not granted by someother being.(Zaati)
Whereas attributes of Everone other Than Allah swt are not azali means not from the beginning,not forever,limited,mortal and granted by Allah Swt not by itself.
So when someone says Ya Ayyuhan Nabi In tasshahud calling to Prophet Muhammad peace be upon him sending Salam considering alive in grave,it is not considered as Shirk at all.
Narrated Abu Huraira: Allah's Messenger (ﷺ) said, "Do you consider or
see that my face is towards the Qibla? By Allah, neither your
submissiveness nor your bowing is hidden from me, surely I see you
from my back."(Bukhari).
Now see this ayah from Surah Taubah verse 128,
لَقَدْ جَاءَكُمْ رَسُولٌ مِنْ أَنْفُسِكُمْ عَزِيزٌ عَلَيْهِ مَا
عَنِتُّمْ حَرِيصٌ عَلَيْكُمْ بِالْمُؤْمِنِينَ رَءُوفٌ رَحِيمٌ Now,
there has come to you a Rasool from among yourselves, the one who
grieves at your loss and who is excessively anxious for your success
in both worlds, and who is compassionate and merciful towards the
believers
Now here we see Allah Swt has stated "Rauf"(رَءُوفٌ) and "Raheem" (رَحِيمٌ) for Prophet Muhammad peace be upon him whereas we know these are the names of Allah swt and his attributes but if the concept and explanation of Shirk fis Sifaat is clear in minds no one would be doubtful as we know that attributes related to Prophet Muhammad peace be upon him is granted by Allah swt ,it was not from the beginning or by himself etc.
Regarding your other concern sending another kind of salawat to be biddah so what kind of salawat is "Mola Ya salli wasallim daiman abadan" every muslim knows it and recite it very well.Majority of Scholars have said your quoted salawat to be permissible.
You could see this too
Allah Swt and His Messenger knows best.
