- Like what you've got: Reconsider. Seriously, newer models will outshoot a D100 in all kinds of ways.
- Dislike what you've got: Upgrade. The D7500 or D500 is the right answer, I believe. You could wimp out and buy a used D300 or D7200, but the bump up in quality is bigger and dramatic with the two cameras I mention (D7500 and D500). A D610, D750, D780, or D850 is a long stretch and would force you to realign your lens selection from DX to FX. Even a D500 is going to have you trying to figure out shot discipline issues that the 6mp sensor was hiding from you.
- Upgrade to mirrorless: Z6III or Z7II, but you’ll be changing from DX to FX lenses.