My mattress creaks at night when I breathe and keeps me awake. Do I need a new mattress?

That or you could try not breathing. >:)

You may need a new mattress but there are other possibilities It could either be your frme or bed or it could be your box spring. Look and see if the frame or bed have tight connections if you can tighten them do so If ok you check you box by putting the mattress on the floor and lay on it and listen for squeaks if there are none it is probably the box spring. For other reasons why you may need a new bed see http://matresses101guide.com/Mattress_Information_Do_I_Need_a_New_Mattress.html Mattress Answer Man

Try oiling the springs. If that doesn't work stop breathing.

Try earplugs if you can stand them. If you cannot and you just plain cannot sleep with the creaking, then you are going to need to get a new mattress. I almost always sleep with earplugs and have for about 20 years due to being a night shifter and/or having noisy neighbors.