Anyone who's self-employed should be professional about it, set up an LLC or corporation of some sort, and pay themselves a salary out of the business' net earn

Anyone who's self-employed should be professional about it, set up an LLC or corporation of some sort, and pay themselves a salary out of the business' net earnings. You pay taxes on the salary, but the business gets a deduction for it, so that's no excuse not to do it this way. And complaining that you can't claim the income as a deductible business expense and available to spend on a mortgage at the same time is just whining: it's a cost of doing business or it's profit in your pocket; you can't have it both ways. If this is too complex, and you want the simplicity of being a self-proprietor, then accept the consequences, including not having documented proof of steady income.