Unmarried Partner non EEA

[Merry10]

I would be grateful to welcome opinions that are best suitable for application under 5years route.
I arrived in the UK to study for a year in 2011, I overstayed. I have a relationship with Italian, I submitted an application in 2015 and I was refused base on 'She is not contributing to NI' as we both self-employed, selling on eBay. She started working a part-time job in other to contribute to NI while I submitted another application and was again refused base on 'No sufficient evidence of cohabitation' and was advised to apply through 5years route.
I would like to know in details which require document is suitable for the 5years route, we have been together for 4years and hope I am also qualified to apply through 5years route.

[Casa]

Is your partner registered with HMRC as self=employed for tax? How long have you been living together in a durable relationship 'akin to marriage'

[Merry10]

Yes, she was registered as self-employed and we do a tax return every year, we have been living together for 4 years till date.