I can read from a score, but without sheet music I am lost
You, readers, are my special friends :) I feel you.
My early piano education focused solely on reading notation and abstract theory, at the expense of ear training and applied theory. For twenty years, while I could "play," I often felt like little more than a human MIDI renderer.
I can help you because I have been where you are. Improvisation was a struggle for me for years. But eventually, through several fortunate circumstances, I made the mental connections that allow me to play my "own" music, free from the tyranny of fully arranged scores. I played piano for decades before I could really play. Benefit from my experience so you don't have put in that much time waiting for these ideas to come together on their own. Let me show you what you're missing to be able to play from fake books, chord charts, or just from your own internal voice.
It's not "magic." I'm living proof that improvisation can be learned. I will guide you through a gradual process that will build the understanding of harmony and melodic tension/resolution, and that will establish the ability to realise at the keys a melody you hear in your head, that improvisatory playing requires.