If your organ improvisations or compositions suffer from the lack of creativity, the solution isn't to figure out some way to invent a lot of musical ideas, figures or more textures. Those are the solutions, based on the notion that what you doing isn't sufficient, isn't interesting and isn't inventive.
The challenge with this approach is that it is very difficult to control it. You can get tons of new ideas, find hundreds of figures in the pieces of other masters but the question is what are you going to do with them? Soon you will get lost in all the wealth of musical material that comes your way.
No, the solution lies in using the musical ideas that you already know and building something interesting out of them. If you only know one chord, that's plenty to start with. Go play with this chord in any key, in any intervalic relationship to find out which solution sounds worth remembering and which one - not so much.
When you do that, when you improvise for 10 minutes just using this chord (regardless if some part of your brain screams at you to stop), then little by little you will discover new interesting ideas and musical elements that you can put in your "bag of tricks".
No, it won't be a perfect sonata or a set of variations that gets listed on the top 10 most important pieces ever written. But yes, you can drammatically solve the problem of "more creativity" by mastering musical elements that you already know and controling them in a creative way.
Everyone is creative. In fact, we are too creative. More important is deciding to use the creativity you already have and share it with others.