Many people have gained a certain amount of skill in sight singing in major keys. They can recognize the sounds of the various notes of the scale in relation to the tonic. But the challenge comes when they encounter minor songs. The intervals are so different, and the tonic doesn't sound like a tonic. How do you conquer the challenge of sight singing in minor keys?
Although this seems like a daunting problem, there is actually a simple solution. Don't consider the tonic as "Do" or 1. Think of it as 6 or "La". This puts "Do" (and the rest of the scale) in the position of the relative major key (three semi-tones higher). All the intervals from this new "Do" sound the same as they did in major, and you can probably sight-sing almost as easily as you did in major, especially after a little practice.
One of the benefits of this approach is that you don't have to identify the song as minor before you start. The key signature identifies the tonic of the relative major, so just sing it if it were in that major key. You won't have to memorize a whole new collection of key signatures for minor keys.
Of course, there are disadvantages as well. You'll have to get used to your melodies ending (and perhaps starting) on "La" instead of "Do". This will seem weird. But you'll get used to it.
There is also the issue of the leading tone, the raised 5th degree, or "Si". This will take some getting used to as well. In my opinion it is better to practice this with the solfege syllables (La, Ti, Do) than the numbers (6, 7, 1) because of the complication of referring to a raised 5 (fee, fi, foe, or maybe fum). It seems easier to just use the standard solfege syllable.
The alternative to using this "La-based" minor reading system is to use "Do" for the tonic in minor as well. Then your scale would be something like: Do Re Me Fa Sol Le Ti Do. The relationships are different; the tendency tones are different, and it seems like a longer learning curve to become proficient. It's also easier to lose track of where "Do" is on the score, since most of us are used to singing with major key signatures.
Take my advice. Make it easy on yourself, and use a La-based system for sight singing in minor keys. You'll find that you'll be able to do it almost as successfully as reading major keys on your first try.