Filing Married Filing Separately is okay, but, as you have discovered, filing jointly usually results in a lower tax. However, you must add your husband's France-based wages to the return if you file jointly.
Since you are using TurboTax, it should not be too hard to add your husband's France-based wages on Line #21 of Form 1040, then fill out Form 1116 (Foreign Tax Credit) to see if the credit given is enough to offset the addtional tax on HIS salary. Note that the Foreign Tax Credit for wages is NOT dollar-for-dollar.
If the calculations result ina refund of $50 or more, then amend your return using Form 1040X and attaching Forms 1040 and 1116.