My proof of living in UK?

[Joao29]

Before submitting my application I was a little bit confused regarding this issue. In many treads on this forum I have seen people saying that the latest self-assessment is sufficient as proof, but I think this is not my case. Let me give you a quick insight into my timeline:

Arrived in the Uk: Aug 2015 (Applied for NIN,UTR and activated it)
1st job (umbrella) Nov 2015-Dec 2015 (tax return 2015-16)
2nd job (umbrella) Feb 2016-Jul 2016 (tax return 2016-17)
3rd job (self employ) Aug 2016-Sep 2017 (tax return 2017-18)
4th job (umbrella) Sep 2017-Oct 2017 (tax return 2018-19)
5th job (self employed) Nov 2017-Sep 2018 (tax return 2019-20)
Went to Uni (MSc) Sep 2018-Sep 2019 (Comprehensive sickness insurance covered this period)
6th job (self employed) sep 2019-present (tax return 2020-21)

I have been working under an umbrella for some time, even if I have had an active UTR since I arrived in the UK and self assessment every single year, will all my self assessments or just last one be enough evidence as my proof of living in UK?

And a quick one, if you are not working for more than 3 months, it is compulsory to have comprehensive sickness insurance. I'm just wondering, is this for not working 3 months in total in a year, 3 months in a row or how it is calculated?

Cheers