Basically, if you are married on or before Dec 31 of the tax year, then your only two filing status choices are Married Filing Joint, or Married Filing Separate. Also understand that for a married couple to file separate will almost always be more costly tax-wise, than filing a joint return will be. That's because when a married couple files separate returns, they are automatically disqualified for deductions and credits they would otherwise qualify for if they filed joint.
As an example (one that I doubt applies to you) if a married couple files separate returns, and if either one or both of them receive social security, then 100% of their social security income is taxable. Whereas if they filed joint, so long as their income was under the threshold, none of it would be taxable.
For example, if your taxable income plus 1/2 of your social security income is between $25,000 and $34,000, you may have to pay income tax on up to 50 percent of your SS benefits. But if that total is more than $34,000 then a maximum of 85 percent of your SS benefits may be taxable. File a separate return there are no limits. 100% of your SS income is taxable. Most likely this example doesn't apply to you. But it's the one I know from memory.
One thing you can do is use the TaxCaster program which will give you rough numbers (very, *very* rough) on what to expect with different filing scenarios. It's at https://turbotax.intuit.com/tax-tools/calculators/taxcaster/
