It will start to get easier very soon. DO NOT change the key - e.g. do not try to visualize G major as A major. This avoids the mental calculus required when reading accidentals - and avoiding extra effort is imperative. Again, leave the key signature be - remember it only in the original key. And like swimming, we will never forget how.
Transposition is like that - exactly.
It becomes easy - even natural in an odd way. Stay with it. And anyone can learn to be good at it. Don't count on that raise at the end of the season. Knowing this, we should not over-rate the issue of transposing a single line, even at sight.