Yes, it is normal for your mattress to form around your body contours. Both natural settlement and frequent turning will reduce compression marks over time.
Our approximate guidelines for natural settlement on turn-able mattresses are as below:
6 months – 1 year: 4cm
1-2 years: 4.5cm
2-7 years: 6cm
7-15 years: 7.5cm
15 years+: 9cm.