Internet through at&t, getting Netflix how many MBPS will I need?

My sister and I are getting our first apartment, apartment goes through AT&T for internet and phone service, I have a netflix account, so we won't worry about getting cable all my favorite shows are on netflix anyway. We both work during the day, my sister isn't into TV much, I work from noon to 9, lay in bed and will keep netflix on all night until work the next morning. We both love the internet, I usually stay on Wifi on my phone, sister uses her laptop. I'm trying to save money and trying to figure out how many mbps I will need to keep netflix running smoothly. 3 mbps is $38 6 mbps is $43, while 12 is $48, I'm sure 12 would be a good deal, but idk if that would be too much for two people to browse the internet and watch netflix all night. We both have jobs where we can browse the internet at work also. So please someone tell me how many netflix would need to run decently. Any info would be greatly appreciated =)