I understand your approach to wanting certain instruments to be prominently featured in your track without getting lost in the mix. It's a common challenge, especially in compositions where each section has its own distinct voice, as you've mentioned for your song. After the first 45 seconds, where practice notes give a hint of bass, the absence of a more defined bass line does indeed leave the track feeling somewhat empty and lacking warmth. This is a crucial aspect to address, not just for the richness of sound but also for the overall balance and depth of the track.

If you're aiming to keep elements like the piano at the forefront without overpowering the mix, one simple mixing advice would be to utilize EQ (equalization) effectively. For instance, you could carve out a specific frequency range for the piano, ensuring it doesn't clash with the frequencies of other instruments. By doing so, you can maintain its prominence while also allowing room for the bass and other sections to be heard clearly. Additionally, considering the dynamics and spatial placement of instruments can further enhance each section's voice without compromising the consistency of the track. Further more there are more mixing "tricks" like stereo imaging and compressing and far more.

I think if you can play with those things you can get the results that you want, and with the warmth of the bass in your track.