God did not tell us to "choose a day that we want to rest". GOD chose "the seventh day".
Some people rationalize that "Well, as long as you take ONE day, it's okay." It IS okay if you are, with all integrity of your heart, doing it in honor of God. But, for those who KNOW the law and UNDERSTAND IT, it is NOT okay to just take ANY day. At that point, taking ANY day becomes willful disobedience.
God said take the 7th day. Keep it HOLY. REST. And, He even gave the reason for it:
God has blessings and cursing for those who profane the Sabbath. Read Leviticus 26. Particularly verse 34>
Read also Ezekial Chapter 20
If you have become convicted and cannot figure a way to honor the Sabbath the way it is stated in these verses, take comfort in the Chapter of Matthew 12, but I BEG you, do not use this to RATIONALIZE that dishonoring the Sabbath is okay.