There is more than one issue rolling around here.
Issue #1: Which day is sabbath.
Sabbath is the seventh day. It begins Friday at sundown and continues until Saturday at sundown. Christians do not worship on the sabbath, but on the Lord's Day, which is a whole other thing. The church did not "change the sabbath to Sunday" so to speak, but simply broke bread on the Lord's Day, the day upon which Christ arose.
Issue #2: Should Christians observe the sabbath?
Certainly the apostles did, but then again they were Jews. The sabbath was given to Israel as a memorial of our exodus from Egypt. Deuteronomy 5:15 "Remember that you were slaves in Egypt and that the LORD your God brought you out of there with a mighty hand and an outstretched arm. Therefore the LORD your God has commanded you to observe the Sabbath day." Gentiles were never delivered from Egypt, and so do not keep the sabbath.
In Acts 15, the whole issue of Gentile converts is discussed, and whether they should be required to keep the Mosaic covenant (which would include keeping the sabbath). The verdict of the Council of Jerusalem is NO, appart from a few universal laws, Gentile converts do not need to become Jews, and do not need to keep any of the Jewish laws (including observing the sabbath).
In conclusion, I would say that you are not obligated to keep the sabbath, since you are not a Jew. However, if you want to keep the sabbath out of love, more power to you! In such a case, keep it from Friday sundown until Saturday Sundown.
You do not need to attend a "sabbath keeping church" to do so. I am Catholic, as well as Jew, and I keep sabbath. I basically refrain from working, lighting fires, etc., on sabbath, and still attend Church on Sunday. No conflict.
