I'm told that mortgage advisors will only count my self employed income (which is more than the employed income) and do affordability based on that
Banks will normally want information on all
taxable income, and most of their systems will allow for multiple income streams when calculating affordability.
As far as FCA/MMR rules are concerned, there is no discriminatory bias towards those who are employed over the self-employed. The onus placed on the lender is to verify your taxable income irrespective of whether that's through employment or self-employment.
Have you explored the possibility of a personal loan? Interest rates are at a historic low.