I would like an example of a mortgage budget letter. The under writer is asking for it.
That's strange, what'd your LO suggest you write? It would be reasonable to ask if you didn't get any guidance imo.
My theory would just do a quick monthly budget exercise and document the line items
Mortgage Payment: -$YYYY
Car payment: -$DDD
<etc for major bits>
= monthly free cash flow.
Out of curiosity what was your DTI?
UW can ask for these if DTI is very high (50%+). They want to know if you will soon be getting a raise, if you have additional income in the household that is not is not on the loan, any major expenses being eliminated soon, etc. Usually helps to explain if you have a clean housing/credit history as well. Your LO should help walk you through this.