Have you tried listening to some classical, orchestral music, especially the cello and double bass lines, or trombones..? Composers such as Saint-Saëns, The Schubert symphonies, Debussy..? There's a lot going on, often with 'simple' lines, but capable of genuine emotion. Listening, rather than studying, at first, just to absorb some of the vocabulary of these instruments in the context of the composition. Much cello work can be used directly on an electric bass, but a lot of music really only makes sense as a whole, not simply from any one instrument (well, maybe Saint-Saëns 'The Carnaval Of The Animals'...)...). Worth a listen..?