British Citizenship

[nvf28]

Hello Everyone,
I appreciate this question has been floated numerous times, however everyone's circumstances are different.
I was born in the UK in 1989 to two European parents, both of whom were 'settled' in the UK before my birth.
They both studied in the UK for a number of years before my birth, and married in the UK.
My mother travelled over with her family in her late teens as her father was transferred over for work. My father came over with IDL. Typically, neither of my parents have any paperwork showing any of the above.
I am trying to prove that I am a British Citizen. Is it easier for me to apply for Naturalisation / to become a citizen, or to try to somehow gather documents from my parents.
From a cost perspective, the latter, but from an ease perspective, I think the former?
How do I prove I was in the UK for the first 10 years of my life - which I was.
I have also married a Brit but I think this route is even more lengthy and expensive?
Any help would be greatly appreciated. I have applied for a passport twice previously and the last hurdle I reached was proving my parents settlement. I was asked to provide their tax documents from 1979, which as you can imagine, they did not hold.
Many thanks