You should be able to do it by using Do Not Disturb (DND) mode.
First, you'll want to go to Settings>Do Not Disturb>Allow Calls From> Select Favorites
Second, if you have the number in your contacts, go to the contact, scroll to the bottom and select "Add to Favorites." If you don't have that number in Contacts, create it. I'd suggest changing the ringtone to a unique ringtone while you're there.
Then when you want to go to bed you can turn on DND by going into Settings>Do Not Disturb and slide the Manual button to the right. Or, the shortcut of swiping up for the control center and clicking the moon button. You should see a moon on the upper right portion of the phone.