Adult dog pulls on the lead/ Is there a solution?

I’m looking for advice and experiences from others because I’m starting to feel stuck.

• Dog: 7-year-old medium Cavachon
• Problem: Pulls on the lead during walks, inconsistent behaviour
• Household: Family of 3, all walk him, which seems to make training harder
• What I’ve tried:
  
  • Slowing down or stopping when he pulls
  • Treats and “sit” cues
  • Harnesses
  • YouTube tutorials / online advice

The worst part has been that walks have become a chore instead of enjoyable. Even my mum has complained of back pain from the pulling: the thing is he’s not a big dog!

I’d love to know:

• Is this a common problem with older dogs?
• Has anyone successfully retrained an adult dog to walk nicely on the lead?
• If so, what approach actually worked?

Any experiences or advice would be hugely appreciated.