I spoke with a tax accountant and was informed that I could file Single. The reason, my spouse doesn't have a social security number or an ITIN. If this applies to you (spouse with no SSN or ITIN) then you can file single...... You won't find it anywhere online (at least not that I could find and I Googled it for hours). The reason the accountant knows this is because they've gotten it in writing.
Wow! I'm left speechless.
I'm not suggesting you do this, but it would be most enlightening if one were to ask for confirmation by viewing the "in writing" document.
I take it this was the first year of filing after the marriage and you filed as single the previous year. Theoretically, filing single or married filing separately will have no difference to thresholds since they are generally the same. And, it's a safe bet your spouse won't have any traceable US income.
You won't find this online since a married person cannot file as single, although bless the US tax system, the varying array of tax preparers in the States, and the infinite interpretations, both fact based or convenience based, one can try anything it seems,.... once. The odds of being audited versus the $150, multiplied by a reasonable number of clients, undoubtedly works in the preparers favour.