As sars has said, there is no possibility to switch from a visitor visa to any form of settlement visa within the UK.
Just based solely on what you've said, I think your best option is to complete a 2 year period living together and use that time to prepare for a settlement visa application.
There's a considerable amount of evidence needed to support an application for the visa and also the claim that you have lived together in a relationship akin to marriage for 2 years.
Your situation may also be complicated by current financial requirements in that you are not yet employed in UK. As the sponsor you need to provide evidence of meeting the financial requirement from your own means. There is no third party financial sponsorhip considered.
Hope this helps