I am about to start learning a group of level 1 pieces in G major, and contemplating on to read them before practice.
Lately when learning new piece in C major, I've tried to sing the melody first (with limited success), and found it helps. The way I was taught singing (not formally, just elementary school stuff) was to use solfège (do re me fa so la ti do). Songs were printed using the numbered musical notation. It is quite easy to associate intervals with these single syllable sounds. And transposing to different key is easy because all that's needed is a different starting pitch.

Now I am learning piano, and the modern staff notation, it's taking me time to get comfortable (I am still not) with the letter alphabets. Especially when trying to sing, I feel letters are not as easily to pronounce quickly as solfège. And how do I speak out sharps and flats in a hurry?
What I am really wondering is when piano players sight read, if they somehow see or think in the way similar to solfège. I've read that people sight read by looking at the intervals rather than individual note. But do you also re-orient to the tonic note of the key signature? For example in a piece in G major, do you look at the notes by noticing their distance to G ledger and therefore their position in the scale. If so, this makes sense to me because that seems to be the same way I practice my scale in G major, and my fingers will just go to the appropriate black key naturally.
I am really interested in what you think and what works for you. Thanks!
https://youtu.be/drnBMAEA3AM