Your new mattress needs time to adjust to your body. Here are a few ways to break in your mattress during your 120 nights to ensure it's perfect:
Let it breathe.
It's tempting to dress it up in new bedding, but give it a few hours to settle and get some oxygen flow.
Put on the pressure.
Try walking around on it gently or using your hands and feet to apply some pressure to loosen it up.
It'll take some time for it to adjust to your body, usually around 3 weeks. Sleep on it every night for a minimum of 21 nights so your mattress can get to know you.