Let me ask you this: How are your harmony skills?
The reason I'm asking this is because they are related to sight-reading skills as well.
With time, if you continue to sight-read organ music, the ability to not look at the keyboard and still play the right notes will become better. But it's a process.
Besides that, having proficiency in harmony will help you understand the music that you play, even the music that you sight-read. Not only you will think in patterns, but you will also know what they mean.
It's like learning a foreign language. You can learn how to pronounce the words in that language and even native speaker can understand you but without knowing what individual words or phrases mean - it will be automatic memorization - sometimes it works, sometimes it doesn't.
I hope this analogy makes sense.
Besides having a decent technique, harmony and analytical skills are a single biggest factor of success in organ playing in general and in sight-reading in particular.
So if you study harmony in parallel to sight-reading, you know you're on the right path.
[HT to Dominique]
Practice ascending diatonic sequence in G minor. The chords: V6-V65-I (see video example below):