In reply to Tonybhoy:
Not very helpful to you, but when I last looked at this, I used it as the perfect excuse for a new bike 😁
Seriously, I think you need a new cassette, deraileur and chain. Depending how many gears your cassette has,, and how much of a gear freak you are, certainly don't dismiss groupsets like Tiagra. They are pretty impressive these days.